Add m-esr52 at 52.6.0

1 files changed, 2466 insertions, 0 deletions

diff --git a/js/xpconnect/wrappers/XrayWrapper.cpp b/js/xpconnect/wrappers/XrayWrapper.cpp
new file mode 100644
index 000000000..5e537692d
--- /dev/null
+++ b/js/xpconnect/wrappers/XrayWrapper.cpp
@@ -0,0 +1,2466 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/* vim: set ts=8 sts=4 et sw=4 tw=99: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "XrayWrapper.h"
+#include "AccessCheck.h"
+#include "WrapperFactory.h"
+
+#include "nsDependentString.h"
+#include "nsIScriptError.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/ScriptSettings.h"
+
+#include "XPCWrapper.h"
+#include "xpcprivate.h"
+
+#include "jsapi.h"
+#include "jsprf.h"
+#include "nsJSUtils.h"
+#include "nsPrintfCString.h"
+
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/WindowBinding.h"
+#include "mozilla/dom/XrayExpandoClass.h"
+#include "nsGlobalWindow.h"
+
+using namespace mozilla::dom;
+using namespace JS;
+using namespace mozilla;
+
+using js::Wrapper;
+using js::BaseProxyHandler;
+using js::IsCrossCompartmentWrapper;
+using js::UncheckedUnwrap;
+using js::CheckedUnwrap;
+
+namespace xpc {
+
+using namespace XrayUtils;
+
+#define Between(x, a, b) (a <= x && x <= b)
+
+static_assert(JSProto_URIError - JSProto_Error == 7, "New prototype added in error object range");
+#define AssertErrorObjectKeyInBounds(key) \
+    static_assert(Between(key, JSProto_Error, JSProto_URIError), "We depend on jsprototypes.h ordering here");
+MOZ_FOR_EACH(AssertErrorObjectKeyInBounds, (),
+             (JSProto_Error, JSProto_InternalError, JSProto_EvalError, JSProto_RangeError,
+              JSProto_ReferenceError, JSProto_SyntaxError, JSProto_TypeError, JSProto_URIError));
+
+static_assert(JSProto_Uint8ClampedArray - JSProto_Int8Array == 8, "New prototype added in typed array range");
+#define AssertTypedArrayKeyInBounds(key) \
+    static_assert(Between(key, JSProto_Int8Array, JSProto_Uint8ClampedArray), "We depend on jsprototypes.h ordering here");
+MOZ_FOR_EACH(AssertTypedArrayKeyInBounds, (),
+             (JSProto_Int8Array, JSProto_Uint8Array, JSProto_Int16Array, JSProto_Uint16Array,
+              JSProto_Int32Array, JSProto_Uint32Array, JSProto_Float32Array, JSProto_Float64Array, JSProto_Uint8ClampedArray));
+
+#undef Between
+
+inline bool
+IsErrorObjectKey(JSProtoKey key)
+{
+    return key >= JSProto_Error && key <= JSProto_URIError;
+}
+
+inline bool
+IsTypedArrayKey(JSProtoKey key)
+{
+    return key >= JSProto_Int8Array && key <= JSProto_Uint8ClampedArray;
+}
+
+// Whitelist for the standard ES classes we can Xray to.
+static bool
+IsJSXraySupported(JSProtoKey key)
+{
+    if (IsTypedArrayKey(key))
+        return true;
+    if (IsErrorObjectKey(key))
+        return true;
+    switch (key) {
+      case JSProto_Date:
+      case JSProto_Object:
+      case JSProto_Array:
+      case JSProto_Function:
+      case JSProto_TypedArray:
+      case JSProto_SavedFrame:
+      case JSProto_RegExp:
+      case JSProto_Promise:
+      case JSProto_ArrayBuffer:
+      case JSProto_SharedArrayBuffer:
+        return true;
+      default:
+        return false;
+    }
+}
+
+XrayType
+GetXrayType(JSObject* obj)
+{
+    obj = js::UncheckedUnwrap(obj, /* stopAtWindowProxy = */ false);
+    if (mozilla::dom::UseDOMXray(obj))
+        return XrayForDOMObject;
+
+    const js::Class* clasp = js::GetObjectClass(obj);
+    if (IS_WN_CLASS(clasp) || js::IsWindowProxy(obj))
+        return XrayForWrappedNative;
+
+    JSProtoKey standardProto = IdentifyStandardInstanceOrPrototype(obj);
+    if (IsJSXraySupported(standardProto))
+        return XrayForJSObject;
+
+    // Modulo a few exceptions, everything else counts as an XrayWrapper to an
+    // opaque object, which means that more-privileged code sees nothing from
+    // the underlying object. This is very important for security. In some cases
+    // though, we need to make an exception for compatibility.
+    if (IsSandbox(obj))
+        return NotXray;
+
+    return XrayForOpaqueObject;
+}
+
+JSObject*
+XrayAwareCalleeGlobal(JSObject* fun)
+{
+  MOZ_ASSERT(js::IsFunctionObject(fun));
+
+  if (!js::FunctionHasNativeReserved(fun)) {
+      // Just a normal function, no Xrays involved.
+      return js::GetGlobalForObjectCrossCompartment(fun);
+  }
+
+  // The functions we expect here have the Xray wrapper they're associated with
+  // in their XRAY_DOM_FUNCTION_PARENT_WRAPPER_SLOT and, in a debug build,
+  // themselves in their XRAY_DOM_FUNCTION_NATIVE_SLOT_FOR_SELF.  Assert that
+  // last bit.
+  MOZ_ASSERT(&js::GetFunctionNativeReserved(fun, XRAY_DOM_FUNCTION_NATIVE_SLOT_FOR_SELF).toObject() ==
+             fun);
+
+  Value v =
+      js::GetFunctionNativeReserved(fun, XRAY_DOM_FUNCTION_PARENT_WRAPPER_SLOT);
+  MOZ_ASSERT(IsXrayWrapper(&v.toObject()));
+
+  JSObject* xrayTarget = js::UncheckedUnwrap(&v.toObject());
+  return js::GetGlobalForObjectCrossCompartment(xrayTarget);
+}
+
+JSObject*
+XrayTraits::getExpandoChain(HandleObject obj)
+{
+    return ObjectScope(obj)->GetExpandoChain(obj);
+}
+
+bool
+XrayTraits::setExpandoChain(JSContext* cx, HandleObject obj, HandleObject chain)
+{
+    return ObjectScope(obj)->SetExpandoChain(cx, obj, chain);
+}
+
+// static
+XPCWrappedNative*
+XPCWrappedNativeXrayTraits::getWN(JSObject* wrapper)
+{
+    return XPCWrappedNative::Get(getTargetObject(wrapper));
+}
+
+const JSClass XPCWrappedNativeXrayTraits::HolderClass = {
+    "NativePropertyHolder", JSCLASS_HAS_RESERVED_SLOTS(2)
+};
+
+
+const JSClass JSXrayTraits::HolderClass = {
+    "JSXrayHolder", JSCLASS_HAS_RESERVED_SLOTS(SLOT_COUNT)
+};
+
+bool
+OpaqueXrayTraits::resolveOwnProperty(JSContext* cx, const Wrapper& jsWrapper, HandleObject wrapper,
+                                     HandleObject holder, HandleId id,
+                                     MutableHandle<PropertyDescriptor> desc)
+{
+    bool ok = XrayTraits::resolveOwnProperty(cx, jsWrapper, wrapper, holder, id, desc);
+    if (!ok || desc.object())
+        return ok;
+
+    return ReportWrapperDenial(cx, id, WrapperDenialForXray, "object is not safely Xrayable");
+}
+
+bool
+ReportWrapperDenial(JSContext* cx, HandleId id, WrapperDenialType type, const char* reason)
+{
+    CompartmentPrivate* priv = CompartmentPrivate::Get(CurrentGlobalOrNull(cx));
+    bool alreadyWarnedOnce = priv->wrapperDenialWarnings[type];
+    priv->wrapperDenialWarnings[type] = true;
+
+    // The browser console warning is only emitted for the first violation,
+    // whereas the (debug-only) NS_WARNING is emitted for each violation.
+#ifndef DEBUG
+    if (alreadyWarnedOnce)
+        return true;
+#endif
+
+    nsAutoJSString propertyName;
+    RootedValue idval(cx);
+    if (!JS_IdToValue(cx, id, &idval))
+        return false;
+    JSString* str = JS_ValueToSource(cx, idval);
+    if (!str)
+        return false;
+    if (!propertyName.init(cx, str))
+        return false;
+    AutoFilename filename;
+    unsigned line = 0, column = 0;
+    DescribeScriptedCaller(cx, &filename, &line, &column);
+
+    // Warn to the terminal for the logs.
+    NS_WARNING(nsPrintfCString("Silently denied access to property %s: %s (@%s:%u:%u)",
+                               NS_LossyConvertUTF16toASCII(propertyName).get(), reason,
+                               filename.get(), line, column).get());
+
+    // If this isn't the first warning on this topic for this global, we've
+    // already bailed out in opt builds. Now that the NS_WARNING is done, bail
+    // out in debug builds as well.
+    if (alreadyWarnedOnce)
+        return true;
+
+    //
+    // Log a message to the console service.
+    //
+
+    // Grab the pieces.
+    nsCOMPtr<nsIConsoleService> consoleService = do_GetService(NS_CONSOLESERVICE_CONTRACTID);
+    NS_ENSURE_TRUE(consoleService, true);
+    nsCOMPtr<nsIScriptError> errorObject = do_CreateInstance(NS_SCRIPTERROR_CONTRACTID);
+    NS_ENSURE_TRUE(errorObject, true);
+
+    // Compute the current window id if any.
+    uint64_t windowId = 0;
+    nsGlobalWindow* win = WindowGlobalOrNull(CurrentGlobalOrNull(cx));
+    if (win)
+      windowId = win->WindowID();
+
+
+    Maybe<nsPrintfCString> errorMessage;
+    if (type == WrapperDenialForXray) {
+        errorMessage.emplace("XrayWrapper denied access to property %s (reason: %s). "
+                             "See https://developer.mozilla.org/en-US/docs/Xray_vision "
+                             "for more information. Note that only the first denied "
+                             "property access from a given global object will be reported.",
+                             NS_LossyConvertUTF16toASCII(propertyName).get(),
+                             reason);
+    } else {
+        MOZ_ASSERT(type == WrapperDenialForCOW);
+        errorMessage.emplace("Security wrapper denied access to property %s on privileged "
+                             "Javascript object. Support for exposing privileged objects "
+                             "to untrusted content via __exposedProps__ is being gradually "
+                             "removed - use WebIDL bindings or Components.utils.cloneInto "
+                             "instead. Note that only the first denied property access from a "
+                             "given global object will be reported.",
+                             NS_LossyConvertUTF16toASCII(propertyName).get());
+    }
+    nsString filenameStr(NS_ConvertASCIItoUTF16(filename.get()));
+    nsresult rv = errorObject->InitWithWindowID(NS_ConvertASCIItoUTF16(errorMessage.ref()),
+                                                filenameStr,
+                                                EmptyString(),
+                                                line, column,
+                                                nsIScriptError::warningFlag,
+                                                "XPConnect",
+                                                windowId);
+    NS_ENSURE_SUCCESS(rv, true);
+    rv = consoleService->LogMessage(errorObject);
+    NS_ENSURE_SUCCESS(rv, true);
+
+    return true;
+}
+
+bool JSXrayTraits::getOwnPropertyFromWrapperIfSafe(JSContext* cx,
+                                                   HandleObject wrapper,
+                                                   HandleId id,
+                                                   MutableHandle<PropertyDescriptor> outDesc)
+{
+    MOZ_ASSERT(js::IsObjectInContextCompartment(wrapper, cx));
+    RootedObject target(cx, getTargetObject(wrapper));
+    {
+        JSAutoCompartment ac(cx, target);
+        if (!getOwnPropertyFromTargetIfSafe(cx, target, wrapper, id, outDesc))
+            return false;
+    }
+    return JS_WrapPropertyDescriptor(cx, outDesc);
+}
+
+bool JSXrayTraits::getOwnPropertyFromTargetIfSafe(JSContext* cx,
+                                                  HandleObject target,
+                                                  HandleObject wrapper,
+                                                  HandleId id,
+                                                  MutableHandle<PropertyDescriptor> outDesc)
+{
+    // Note - This function operates in the target compartment, because it
+    // avoids a bunch of back-and-forth wrapping in enumerateNames.
+    MOZ_ASSERT(getTargetObject(wrapper) == target);
+    MOZ_ASSERT(js::IsObjectInContextCompartment(target, cx));
+    MOZ_ASSERT(WrapperFactory::IsXrayWrapper(wrapper));
+    MOZ_ASSERT(outDesc.object() == nullptr);
+
+    Rooted<PropertyDescriptor> desc(cx);
+    if (!JS_GetOwnPropertyDescriptorById(cx, target, id, &desc))
+        return false;
+
+    // If the property doesn't exist at all, we're done.
+    if (!desc.object())
+        return true;
+
+    // Disallow accessor properties.
+    if (desc.hasGetterOrSetter()) {
+        JSAutoCompartment ac(cx, wrapper);
+        return ReportWrapperDenial(cx, id, WrapperDenialForXray, "property has accessor");
+    }
+
+    // Apply extra scrutiny to objects.
+    if (desc.value().isObject()) {
+        RootedObject propObj(cx, js::UncheckedUnwrap(&desc.value().toObject()));
+        JSAutoCompartment ac(cx, propObj);
+
+        // Disallow non-subsumed objects.
+        if (!AccessCheck::subsumes(target, propObj)) {
+            JSAutoCompartment ac(cx, wrapper);
+            return ReportWrapperDenial(cx, id, WrapperDenialForXray, "value not same-origin with target");
+        }
+
+        // Disallow non-Xrayable objects.
+        XrayType xrayType = GetXrayType(propObj);
+        if (xrayType == NotXray || xrayType == XrayForOpaqueObject) {
+            JSAutoCompartment ac(cx, wrapper);
+            return ReportWrapperDenial(cx, id, WrapperDenialForXray, "value not Xrayable");
+        }
+
+        // Disallow callables.
+        if (JS::IsCallable(propObj)) {
+            JSAutoCompartment ac(cx, wrapper);
+            return ReportWrapperDenial(cx, id, WrapperDenialForXray, "value is callable");
+        }
+    }
+
+    // Disallow any property that shadows something on its (Xrayed)
+    // prototype chain.
+    JSAutoCompartment ac2(cx, wrapper);
+    RootedObject proto(cx);
+    bool foundOnProto = false;
+    if (!JS_GetPrototype(cx, wrapper, &proto) ||
+        (proto && !JS_HasPropertyById(cx, proto, id, &foundOnProto)))
+    {
+        return false;
+    }
+    if (foundOnProto)
+        return ReportWrapperDenial(cx, id, WrapperDenialForXray, "value shadows a property on the standard prototype");
+
+    // We made it! Assign over the descriptor, and don't forget to wrap.
+    outDesc.assign(desc.get());
+    return true;
+}
+
+// Returns true on success (in the JSAPI sense), false on failure.  If true is
+// returned, desc.object() will indicate whether we actually resolved
+// the property.
+//
+// id is the property id we're looking for.
+// holder is the object to define the property on.
+// fs is the relevant JSFunctionSpec*.
+// ps is the relevant JSPropertySpec*.
+// desc is the descriptor we're resolving into.
+static bool
+TryResolvePropertyFromSpecs(JSContext* cx, HandleId id, HandleObject holder,
+                            const JSFunctionSpec* fs,
+                            const JSPropertySpec* ps,
+                            MutableHandle<PropertyDescriptor> desc)
+{
+    // Scan through the functions.
+    const JSFunctionSpec* fsMatch = nullptr;
+    for ( ; fs && fs->name; ++fs) {
+        if (PropertySpecNameEqualsId(fs->name, id)) {
+            fsMatch = fs;
+            break;
+        }
+    }
+    if (fsMatch) {
+        // Generate an Xrayed version of the method.
+        RootedFunction fun(cx, JS::NewFunctionFromSpec(cx, fsMatch, id));
+        if (!fun)
+            return false;
+
+        // The generic Xray machinery only defines non-own properties of the target on
+        // the holder. This is broken, and will be fixed at some point, but for now we
+        // need to cache the value explicitly. See the corresponding call to
+        // JS_GetOwnPropertyDescriptorById at the top of
+        // JSXrayTraits::resolveOwnProperty.
+        RootedObject funObj(cx, JS_GetFunctionObject(fun));
+        return JS_DefinePropertyById(cx, holder, id, funObj, 0) &&
+               JS_GetOwnPropertyDescriptorById(cx, holder, id, desc);
+    }
+
+    // Scan through the properties.
+    const JSPropertySpec* psMatch = nullptr;
+    for ( ; ps && ps->name; ++ps) {
+        if (PropertySpecNameEqualsId(ps->name, id)) {
+            psMatch = ps;
+            break;
+        }
+    }
+    if (psMatch) {
+        desc.value().setUndefined();
+        RootedFunction getterObj(cx);
+        RootedFunction setterObj(cx);
+        unsigned flags = psMatch->flags;
+        if (psMatch->isAccessor()) {
+            if (psMatch->isSelfHosted()) {
+                getterObj = JS::GetSelfHostedFunction(cx, psMatch->accessors.getter.selfHosted.funname, id, 0);
+                if (!getterObj)
+                    return false;
+                desc.setGetterObject(JS_GetFunctionObject(getterObj));
+                if (psMatch->accessors.setter.selfHosted.funname) {
+                    MOZ_ASSERT(flags & JSPROP_SETTER);
+                    setterObj = JS::GetSelfHostedFunction(cx, psMatch->accessors.setter.selfHosted.funname, id, 0);
+                    if (!setterObj)
+                        return false;
+                    desc.setSetterObject(JS_GetFunctionObject(setterObj));
+                }
+            } else {
+                desc.setGetter(JS_CAST_NATIVE_TO(psMatch->accessors.getter.native.op,
+                                                 JSGetterOp));
+                desc.setSetter(JS_CAST_NATIVE_TO(psMatch->accessors.setter.native.op,
+                                                 JSSetterOp));
+            }
+            desc.setAttributes(flags);
+        } else {
+            RootedValue v(cx);
+            if (!psMatch->getValue(cx, &v))
+                return false;
+            desc.value().set(v);
+            desc.setAttributes(flags & ~JSPROP_INTERNAL_USE_BIT);
+        }
+
+        // The generic Xray machinery only defines non-own properties on the holder.
+        // This is broken, and will be fixed at some point, but for now we need to
+        // cache the value explicitly. See the corresponding call to
+        // JS_GetPropertyById at the top of JSXrayTraits::resolveOwnProperty.
+        //
+        // Note also that the public-facing API here doesn't give us a way to
+        // pass along JITInfo. It's probably ok though, since Xrays are already
+        // pretty slow.
+        return JS_DefinePropertyById(cx, holder, id,
+                                     desc.value(),
+                                     // This particular descriptor, unlike most,
+                                     // actually stores JSNatives directly,
+                                     // since we just set it up.  Do NOT pass
+                                     // JSPROP_PROPOP_ACCESSORS here!
+                                     desc.attributes(),
+                                     JS_PROPERTYOP_GETTER(desc.getter()),
+                                     JS_PROPERTYOP_SETTER(desc.setter())) &&
+               JS_GetOwnPropertyDescriptorById(cx, holder, id, desc);
+    }
+
+    return true;
+}
+
+static bool
+ShouldResolveStaticProperties(JSProtoKey key)
+{
+    // Don't try to resolve static properties on RegExp, because they
+    // have issues.  In particular, some of them grab state off the
+    // global of the RegExp constructor that describes the last regexp
+    // evaluation in that global, which is not a useful thing to do
+    // over Xrays.
+    return key != JSProto_RegExp;
+}
+
+bool
+JSXrayTraits::resolveOwnProperty(JSContext* cx, const Wrapper& jsWrapper,
+                                 HandleObject wrapper, HandleObject holder,
+                                 HandleId id,
+                                 MutableHandle<PropertyDescriptor> desc)
+{
+    // Call the common code.
+    bool ok = XrayTraits::resolveOwnProperty(cx, jsWrapper, wrapper, holder,
+                                             id, desc);
+    if (!ok || desc.object())
+        return ok;
+
+    // The non-HasPrototypes semantics implemented by traditional Xrays are kind
+    // of broken with respect to |own|-ness and the holder. The common code
+    // muddles through by only checking the holder for non-|own| lookups, but
+    // that doesn't work for us. So we do an explicit holder check here, and hope
+    // that this mess gets fixed up soon.
+    if (!JS_GetOwnPropertyDescriptorById(cx, holder, id, desc))
+        return false;
+    if (desc.object()) {
+        desc.object().set(wrapper);
+        return true;
+    }
+
+    RootedObject target(cx, getTargetObject(wrapper));
+    JSProtoKey key = getProtoKey(holder);
+    if (!isPrototype(holder)) {
+        // For Object and Array instances, we expose some properties from the
+        // underlying object, but only after filtering them carefully.
+        //
+        // Note that, as far as JS observables go, Arrays are just Objects with
+        // a different prototype and a magic (own, non-configurable) |.length| that
+        // serves as a non-tight upper bound on |own| indexed properties. So while
+        // it's tempting to try to impose some sort of structure on what Arrays
+        // "should" look like over Xrays, the underlying object is squishy enough
+        // that it makes sense to just treat them like Objects for Xray purposes.
+        if (key == JSProto_Object || key == JSProto_Array) {
+            return getOwnPropertyFromWrapperIfSafe(cx, wrapper, id, desc);
+        } else if (IsTypedArrayKey(key)) {
+            if (IsArrayIndex(GetArrayIndexFromId(cx, id))) {
+                // WebExtensions can't use cloneInto(), so we just let them do
+                // the slow thing to maximize compatibility.
+                if (CompartmentPrivate::Get(CurrentGlobalOrNull(cx))->isWebExtensionContentScript) {
+                    Rooted<PropertyDescriptor> innerDesc(cx);
+                    {
+                        JSAutoCompartment ac(cx, target);
+                        if (!JS_GetOwnPropertyDescriptorById(cx, target, id, &innerDesc))
+                            return false;
+                    }
+                    if (innerDesc.isDataDescriptor() && innerDesc.value().isNumber()) {
+                        desc.setValue(innerDesc.value());
+                        desc.object().set(wrapper);
+                    }
+                    return true;
+                } else {
+                    JS_ReportErrorASCII(cx, "Accessing TypedArray data over Xrays is slow, and forbidden "
+                                        "in order to encourage performant code. To copy TypedArrays "
+                                        "across origin boundaries, consider using Components.utils.cloneInto().");
+                    return false;
+                }
+            }
+        } else if (key == JSProto_Function) {
+            if (id == GetJSIDByIndex(cx, XPCJSContext::IDX_LENGTH)) {
+                FillPropertyDescriptor(desc, wrapper, JSPROP_PERMANENT | JSPROP_READONLY,
+                                       NumberValue(JS_GetFunctionArity(JS_GetObjectFunction(target))));
+                return true;
+            } else if (id == GetJSIDByIndex(cx, XPCJSContext::IDX_NAME)) {
+                RootedString fname(cx, JS_GetFunctionId(JS_GetObjectFunction(target)));
+                FillPropertyDescriptor(desc, wrapper, JSPROP_PERMANENT | JSPROP_READONLY,
+                                       fname ? StringValue(fname) : JS_GetEmptyStringValue(cx));
+            } else {
+                // Look for various static properties/methods and the
+                // 'prototype' property.
+                JSProtoKey standardConstructor = constructorFor(holder);
+                if (standardConstructor != JSProto_Null) {
+                    // Handle the 'prototype' property to make
+                    // xrayedGlobal.StandardClass.prototype work.
+                    if (id == GetJSIDByIndex(cx, XPCJSContext::IDX_PROTOTYPE)) {
+                        RootedObject standardProto(cx);
+                        {
+                            JSAutoCompartment ac(cx, target);
+                            if (!JS_GetClassPrototype(cx, standardConstructor, &standardProto))
+                                return false;
+                            MOZ_ASSERT(standardProto);
+                        }
+
+                        if (!JS_WrapObject(cx, &standardProto))
+                            return false;
+                        FillPropertyDescriptor(desc, wrapper, JSPROP_PERMANENT | JSPROP_READONLY,
+                                               ObjectValue(*standardProto));
+                        return true;
+                    }
+
+                    if (ShouldResolveStaticProperties(standardConstructor)) {
+                        const js::Class* clasp = js::ProtoKeyToClass(standardConstructor);
+                        MOZ_ASSERT(clasp->specDefined());
+
+                        if (!TryResolvePropertyFromSpecs(cx, id, holder,
+                               clasp->specConstructorFunctions(),
+                               clasp->specConstructorProperties(), desc)) {
+                            return false;
+                        }
+
+                        if (desc.object()) {
+                            desc.object().set(wrapper);
+                            return true;
+                        }
+                    }
+                }
+            }
+        } else if (IsErrorObjectKey(key)) {
+            // The useful state of error objects (except for .stack) is
+            // (unfortunately) represented as own data properties per-spec. This
+            // means that we can't have a a clean representation of the data
+            // (free from tampering) without doubling the slots of Error
+            // objects, which isn't great. So we forward these properties to the
+            // underlying object and then just censor any values with the wrong
+            // type. This limits the ability of content to do anything all that
+            // confusing.
+            bool isErrorIntProperty =
+                id == GetJSIDByIndex(cx, XPCJSContext::IDX_LINENUMBER) ||
+                id == GetJSIDByIndex(cx, XPCJSContext::IDX_COLUMNNUMBER);
+            bool isErrorStringProperty =
+                id == GetJSIDByIndex(cx, XPCJSContext::IDX_FILENAME) ||
+                id == GetJSIDByIndex(cx, XPCJSContext::IDX_MESSAGE);
+            if (isErrorIntProperty || isErrorStringProperty) {
+                RootedObject waiver(cx, wrapper);
+                if (!WrapperFactory::WaiveXrayAndWrap(cx, &waiver))
+                    return false;
+                if (!JS_GetOwnPropertyDescriptorById(cx, waiver, id, desc))
+                    return false;
+                bool valueMatchesType = (isErrorIntProperty && desc.value().isInt32()) ||
+                                        (isErrorStringProperty && desc.value().isString());
+                if (desc.hasGetterOrSetter() || !valueMatchesType)
+                    FillPropertyDescriptor(desc, nullptr, 0, UndefinedValue());
+                return true;
+            }
+        } else if (key == JSProto_RegExp) {
+            if (id == GetJSIDByIndex(cx, XPCJSContext::IDX_LASTINDEX))
+                return getOwnPropertyFromWrapperIfSafe(cx, wrapper, id, desc);
+        }
+
+        // The rest of this function applies only to prototypes.
+        return true;
+    }
+
+    // Handle the 'constructor' property.
+    if (id == GetJSIDByIndex(cx, XPCJSContext::IDX_CONSTRUCTOR)) {
+        RootedObject constructor(cx);
+        {
+            JSAutoCompartment ac(cx, target);
+            if (!JS_GetClassObject(cx, key, &constructor))
+                return false;
+        }
+        if (!JS_WrapObject(cx, &constructor))
+            return false;
+        desc.object().set(wrapper);
+        desc.setAttributes(0);
+        desc.setGetter(nullptr);
+        desc.setSetter(nullptr);
+        desc.value().setObject(*constructor);
+        return true;
+    }
+
+    // Handle the 'name' property for error prototypes.
+    if (IsErrorObjectKey(key) && id == GetJSIDByIndex(cx, XPCJSContext::IDX_NAME)) {
+        RootedId className(cx);
+        ProtoKeyToId(cx, key, &className);
+        FillPropertyDescriptor(desc, wrapper, 0, UndefinedValue());
+        return JS_IdToValue(cx, className, desc.value());
+    }
+
+    // Handle the 'lastIndex' property for RegExp prototypes.
+    if (key == JSProto_RegExp && id == GetJSIDByIndex(cx, XPCJSContext::IDX_LASTINDEX))
+        return getOwnPropertyFromWrapperIfSafe(cx, wrapper, id, desc);
+
+    // Grab the JSClass. We require all Xrayable classes to have a ClassSpec.
+    const js::Class* clasp = js::GetObjectClass(target);
+    MOZ_ASSERT(clasp->specDefined());
+
+    // Indexed array properties are handled above, so we can just work with the
+    // class spec here.
+    if (!TryResolvePropertyFromSpecs(cx, id, holder,
+                                     clasp->specPrototypeFunctions(),
+                                     clasp->specPrototypeProperties(),
+                                     desc)) {
+        return false;
+    }
+
+    if (desc.object()) {
+        desc.object().set(wrapper);
+    }
+
+    return true;
+}
+
+bool
+JSXrayTraits::delete_(JSContext* cx, HandleObject wrapper, HandleId id, ObjectOpResult& result)
+{
+    RootedObject holder(cx, ensureHolder(cx, wrapper));
+
+    // If we're using Object Xrays, we allow callers to attempt to delete any
+    // property from the underlying object that they are able to resolve. Note
+    // that this deleting may fail if the property is non-configurable.
+    JSProtoKey key = getProtoKey(holder);
+    bool isObjectOrArrayInstance = (key == JSProto_Object || key == JSProto_Array) &&
+                                   !isPrototype(holder);
+    if (isObjectOrArrayInstance) {
+        RootedObject target(cx, getTargetObject(wrapper));
+        JSAutoCompartment ac(cx, target);
+        Rooted<PropertyDescriptor> desc(cx);
+        if (!getOwnPropertyFromTargetIfSafe(cx, target, wrapper, id, &desc))
+            return false;
+        if (desc.object())
+            return JS_DeletePropertyById(cx, target, id, result);
+    }
+    return result.succeed();
+}
+
+bool
+JSXrayTraits::defineProperty(JSContext* cx, HandleObject wrapper, HandleId id,
+                             Handle<PropertyDescriptor> desc,
+                             Handle<PropertyDescriptor> existingDesc,
+                             ObjectOpResult& result,
+                             bool* defined)
+{
+    *defined = false;
+    RootedObject holder(cx, ensureHolder(cx, wrapper));
+    if (!holder)
+        return false;
+
+
+    // Object and Array instances are special. For those cases, we forward property
+    // definitions to the underlying object if the following conditions are met:
+    // * The property being defined is a value-prop.
+    // * The property being defined is either a primitive or subsumed by the target.
+    // * As seen from the Xray, any existing property that we would overwrite is an
+    //   |own| value-prop.
+    //
+    // To avoid confusion, we disallow expandos on Object and Array instances, and
+    // therefore raise an exception here if the above conditions aren't met.
+    JSProtoKey key = getProtoKey(holder);
+    bool isInstance = !isPrototype(holder);
+    bool isObjectOrArray = (key == JSProto_Object || key == JSProto_Array);
+    if (isObjectOrArray && isInstance) {
+        RootedObject target(cx, getTargetObject(wrapper));
+        if (desc.hasGetterOrSetter()) {
+            JS_ReportErrorASCII(cx, "Not allowed to define accessor property on [Object] or [Array] XrayWrapper");
+            return false;
+        }
+        if (desc.value().isObject() &&
+            !AccessCheck::subsumes(target, js::UncheckedUnwrap(&desc.value().toObject())))
+        {
+            JS_ReportErrorASCII(cx, "Not allowed to define cross-origin object as property on [Object] or [Array] XrayWrapper");
+            return false;
+        }
+        if (existingDesc.hasGetterOrSetter()) {
+            JS_ReportErrorASCII(cx, "Not allowed to overwrite accessor property on [Object] or [Array] XrayWrapper");
+            return false;
+        }
+        if (existingDesc.object() && existingDesc.object() != wrapper) {
+            JS_ReportErrorASCII(cx, "Not allowed to shadow non-own Xray-resolved property on [Object] or [Array] XrayWrapper");
+            return false;
+        }
+
+        Rooted<PropertyDescriptor> wrappedDesc(cx, desc);
+        JSAutoCompartment ac(cx, target);
+        if (!JS_WrapPropertyDescriptor(cx, &wrappedDesc) ||
+            !JS_DefinePropertyById(cx, target, id, wrappedDesc, result))
+        {
+            return false;
+        }
+        *defined = true;
+        return true;
+    }
+
+    // For WebExtensions content scripts, we forward the definition of indexed properties. By
+    // validating that the key and value are both numbers, we can avoid doing any wrapping.
+    if (isInstance && IsTypedArrayKey(key) &&
+        CompartmentPrivate::Get(JS::CurrentGlobalOrNull(cx))->isWebExtensionContentScript &&
+        desc.isDataDescriptor() && (desc.value().isNumber() || desc.value().isUndefined()) &&
+        IsArrayIndex(GetArrayIndexFromId(cx, id)))
+    {
+        RootedObject target(cx, getTargetObject(wrapper));
+        JSAutoCompartment ac(cx, target);
+        if (!JS_DefinePropertyById(cx, target, id, desc, result))
+            return false;
+        *defined = true;
+        return true;
+    }
+
+    return true;
+}
+
+static bool
+MaybeAppend(jsid id, unsigned flags, AutoIdVector& props)
+{
+    MOZ_ASSERT(!(flags & JSITER_SYMBOLSONLY));
+    if (!(flags & JSITER_SYMBOLS) && JSID_IS_SYMBOL(id))
+        return true;
+    return props.append(id);
+}
+
+// Append the names from the given function and property specs to props.
+static bool
+AppendNamesFromFunctionAndPropertySpecs(JSContext* cx,
+                                        const JSFunctionSpec* fs,
+                                        const JSPropertySpec* ps,
+                                        unsigned flags,
+                                        AutoIdVector& props)
+{
+    // Convert the method and property names to jsids and pass them to the caller.
+    for ( ; fs && fs->name; ++fs) {
+        jsid id;
+        if (!PropertySpecNameToPermanentId(cx, fs->name, &id))
+            return false;
+        if (!MaybeAppend(id, flags, props))
+            return false;
+    }
+    for ( ; ps && ps->name; ++ps) {
+        jsid id;
+        if (!PropertySpecNameToPermanentId(cx, ps->name, &id))
+            return false;
+        if (!MaybeAppend(id, flags, props))
+            return false;
+    }
+
+    return true;
+}
+
+bool
+JSXrayTraits::enumerateNames(JSContext* cx, HandleObject wrapper, unsigned flags,
+                             AutoIdVector& props)
+{
+    RootedObject target(cx, getTargetObject(wrapper));
+    RootedObject holder(cx, ensureHolder(cx, wrapper));
+    if (!holder)
+        return false;
+
+    JSProtoKey key = getProtoKey(holder);
+    if (!isPrototype(holder)) {
+        // For Object and Array instances, we expose some properties from the underlying
+        // object, but only after filtering them carefully.
+        if (key == JSProto_Object || key == JSProto_Array) {
+            MOZ_ASSERT(props.empty());
+            {
+                JSAutoCompartment ac(cx, target);
+                AutoIdVector targetProps(cx);
+                if (!js::GetPropertyKeys(cx, target, flags | JSITER_OWNONLY, &targetProps))
+                    return false;
+                // Loop over the properties, and only pass along the ones that
+                // we determine to be safe.
+                if (!props.reserve(targetProps.length()))
+                    return false;
+                for (size_t i = 0; i < targetProps.length(); ++i) {
+                    Rooted<PropertyDescriptor> desc(cx);
+                    RootedId id(cx, targetProps[i]);
+                    if (!getOwnPropertyFromTargetIfSafe(cx, target, wrapper, id, &desc))
+                        return false;
+                    if (desc.object())
+                        props.infallibleAppend(id);
+                }
+            }
+            return true;
+        } else if (IsTypedArrayKey(key)) {
+            uint32_t length = JS_GetTypedArrayLength(target);
+            // TypedArrays enumerate every indexed property in range, but
+            // |length| is a getter that lives on the proto, like it should be.
+            if (!props.reserve(length))
+                return false;
+            for (int32_t i = 0; i <= int32_t(length - 1); ++i)
+                props.infallibleAppend(INT_TO_JSID(i));
+        } else if (key == JSProto_Function) {
+            if (!props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_LENGTH)))
+                return false;
+            if (!props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_NAME)))
+                return false;
+            // Handle the .prototype property and static properties on standard
+            // constructors.
+            JSProtoKey standardConstructor = constructorFor(holder);
+            if (standardConstructor != JSProto_Null) {
+                if (!props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_PROTOTYPE)))
+                    return false;
+
+                if (ShouldResolveStaticProperties(standardConstructor)) {
+                    const js::Class* clasp = js::ProtoKeyToClass(standardConstructor);
+                    MOZ_ASSERT(clasp->specDefined());
+
+                    if (!AppendNamesFromFunctionAndPropertySpecs(
+                           cx, clasp->specConstructorFunctions(),
+                           clasp->specConstructorProperties(), flags, props)) {
+                        return false;
+                    }
+                }
+            }
+        } else if (IsErrorObjectKey(key)) {
+            if (!props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_FILENAME)) ||
+                !props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_LINENUMBER)) ||
+                !props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_COLUMNNUMBER)) ||
+                !props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_STACK)) ||
+                !props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_MESSAGE)))
+            {
+                return false;
+            }
+        } else if (key == JSProto_RegExp) {
+            if (!props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_LASTINDEX)))
+                return false;
+        }
+
+        // The rest of this function applies only to prototypes.
+        return true;
+    }
+
+    // Add the 'constructor' property.
+    if (!props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_CONSTRUCTOR)))
+        return false;
+
+    // For Error protoypes, add the 'name' property.
+    if (IsErrorObjectKey(key) && !props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_NAME)))
+        return false;
+
+    // For RegExp protoypes, add the 'lastIndex' property.
+    if (key == JSProto_RegExp && !props.append(GetJSIDByIndex(cx, XPCJSContext::IDX_LASTINDEX)))
+        return false;
+
+    // Grab the JSClass. We require all Xrayable classes to have a ClassSpec.
+    const js::Class* clasp = js::GetObjectClass(target);
+    MOZ_ASSERT(clasp->specDefined());
+
+    return AppendNamesFromFunctionAndPropertySpecs(
+        cx, clasp->specPrototypeFunctions(),
+        clasp->specPrototypeProperties(), flags, props);
+}
+
+bool
+JSXrayTraits::construct(JSContext* cx, HandleObject wrapper,
+                        const JS::CallArgs& args, const js::Wrapper& baseInstance)
+{
+    JSXrayTraits& self = JSXrayTraits::singleton;
+    JS::RootedObject holder(cx, self.ensureHolder(cx, wrapper));
+    if (self.getProtoKey(holder) == JSProto_Function) {
+        JSProtoKey standardConstructor = constructorFor(holder);
+        if (standardConstructor == JSProto_Null)
+            return baseInstance.construct(cx, wrapper, args);
+
+        const js::Class* clasp = js::ProtoKeyToClass(standardConstructor);
+        MOZ_ASSERT(clasp);
+        if (!(clasp->flags & JSCLASS_HAS_XRAYED_CONSTRUCTOR))
+            return baseInstance.construct(cx, wrapper, args);
+
+        // If the JSCLASS_HAS_XRAYED_CONSTRUCTOR flag is set on the Class,
+        // we don't use the constructor at hand. Instead, we retrieve the
+        // equivalent standard constructor in the xray compartment and run
+        // it in that compartment. The newTarget isn't unwrapped, and the
+        // constructor has to be able to detect and handle this situation.
+        // See the comments in js/public/Class.h and PromiseConstructor for
+        // details and an example.
+        RootedObject ctor(cx);
+        if (!JS_GetClassObject(cx, standardConstructor, &ctor))
+            return false;
+
+        RootedValue ctorVal(cx, ObjectValue(*ctor));
+        HandleValueArray vals(args);
+        RootedObject result(cx);
+        if (!JS::Construct(cx, ctorVal, wrapper, vals, &result))
+            return false;
+        AssertSameCompartment(cx, result);
+        args.rval().setObject(*result);
+        return true;
+    }
+
+    JS::RootedValue v(cx, JS::ObjectValue(*wrapper));
+    js::ReportIsNotFunction(cx, v);
+    return false;
+}
+
+JSObject*
+JSXrayTraits::createHolder(JSContext* cx, JSObject* wrapper)
+{
+    RootedObject target(cx, getTargetObject(wrapper));
+    RootedObject holder(cx, JS_NewObjectWithGivenProto(cx, &HolderClass,
+                                                       nullptr));
+    if (!holder)
+        return nullptr;
+
+    // Compute information about the target.
+    bool isPrototype = false;
+    JSProtoKey key = IdentifyStandardInstance(target);
+    if (key == JSProto_Null) {
+        isPrototype = true;
+        key = IdentifyStandardPrototype(target);
+    }
+    MOZ_ASSERT(key != JSProto_Null);
+
+    // Store it on the holder.
+    RootedValue v(cx);
+    v.setNumber(static_cast<uint32_t>(key));
+    js::SetReservedSlot(holder, SLOT_PROTOKEY, v);
+    v.setBoolean(isPrototype);
+    js::SetReservedSlot(holder, SLOT_ISPROTOTYPE, v);
+
+    // If this is a function, also compute whether it serves as a constructor
+    // for a standard class.
+    if (key == JSProto_Function) {
+        v.setNumber(static_cast<uint32_t>(IdentifyStandardConstructor(target)));
+        js::SetReservedSlot(holder, SLOT_CONSTRUCTOR_FOR, v);
+    }
+
+    return holder;
+}
+
+XPCWrappedNativeXrayTraits XPCWrappedNativeXrayTraits::singleton;
+DOMXrayTraits DOMXrayTraits::singleton;
+JSXrayTraits JSXrayTraits::singleton;
+OpaqueXrayTraits OpaqueXrayTraits::singleton;
+
+XrayTraits*
+GetXrayTraits(JSObject* obj)
+{
+    switch (GetXrayType(obj)) {
+      case XrayForDOMObject:
+        return &DOMXrayTraits::singleton;
+      case XrayForWrappedNative:
+        return &XPCWrappedNativeXrayTraits::singleton;
+      case XrayForJSObject:
+        return &JSXrayTraits::singleton;
+      case XrayForOpaqueObject:
+        return &OpaqueXrayTraits::singleton;
+      default:
+        return nullptr;
+    }
+}
+
+/*
+ * Xray expando handling.
+ *
+ * We hang expandos for Xray wrappers off a reserved slot on the target object
+ * so that same-origin compartments can share expandos for a given object. We
+ * have a linked list of expando objects, one per origin. The properties on these
+ * objects are generally wrappers pointing back to the compartment that applied
+ * them.
+ *
+ * The expando objects should _never_ be exposed to script. The fact that they
+ * live in the target compartment is a detail of the implementation, and does
+ * not imply that code in the target compartment should be allowed to inspect
+ * them. They are private to the origin that placed them.
+ */
+
+static nsIPrincipal*
+ObjectPrincipal(JSObject* obj)
+{
+    return GetCompartmentPrincipal(js::GetObjectCompartment(obj));
+}
+
+static nsIPrincipal*
+GetExpandoObjectPrincipal(JSObject* expandoObject)
+{
+    Value v = JS_GetReservedSlot(expandoObject, JSSLOT_EXPANDO_ORIGIN);
+    return static_cast<nsIPrincipal*>(v.toPrivate());
+}
+
+static void
+ExpandoObjectFinalize(JSFreeOp* fop, JSObject* obj)
+{
+    // Release the principal.
+    nsIPrincipal* principal = GetExpandoObjectPrincipal(obj);
+    NS_RELEASE(principal);
+}
+
+const JSClassOps XrayExpandoObjectClassOps = {
+    nullptr, nullptr, nullptr, nullptr,
+    nullptr, nullptr, nullptr, ExpandoObjectFinalize
+};
+
+bool
+XrayTraits::expandoObjectMatchesConsumer(JSContext* cx,
+                                         HandleObject expandoObject,
+                                         nsIPrincipal* consumerOrigin,
+                                         HandleObject exclusiveGlobal)
+{
+    MOZ_ASSERT(js::IsObjectInContextCompartment(expandoObject, cx));
+
+    // First, compare the principals.
+    nsIPrincipal* o = GetExpandoObjectPrincipal(expandoObject);
+    // Note that it's very important here to ignore document.domain. We
+    // pull the principal for the expando object off of the first consumer
+    // for a given origin, and freely share the expandos amongst multiple
+    // same-origin consumers afterwards. However, this means that we have
+    // no way to know whether _all_ consumers have opted in to collaboration
+    // by explicitly setting document.domain. So we just mandate that expando
+    // sharing is unaffected by it.
+    if (!consumerOrigin->Equals(o))
+      return false;
+
+    // Sandboxes want exclusive expando objects.
+    JSObject* owner = JS_GetReservedSlot(expandoObject,
+                                         JSSLOT_EXPANDO_EXCLUSIVE_GLOBAL)
+                                        .toObjectOrNull();
+    if (!owner && !exclusiveGlobal)
+        return true;
+
+    // The exclusive global should always be wrapped in the target's compartment.
+    MOZ_ASSERT(!exclusiveGlobal || js::IsObjectInContextCompartment(exclusiveGlobal, cx));
+    MOZ_ASSERT(!owner || js::IsObjectInContextCompartment(owner, cx));
+    return owner == exclusiveGlobal;
+}
+
+bool
+XrayTraits::getExpandoObjectInternal(JSContext* cx, HandleObject target,
+                                     nsIPrincipal* origin,
+                                     JSObject* exclusiveGlobalArg,
+                                     MutableHandleObject expandoObject)
+{
+    MOZ_ASSERT(!JS_IsExceptionPending(cx));
+    expandoObject.set(nullptr);
+
+    // The expando object lives in the compartment of the target, so all our
+    // work needs to happen there.
+    RootedObject exclusiveGlobal(cx, exclusiveGlobalArg);
+    JSAutoCompartment ac(cx, target);
+    if (!JS_WrapObject(cx, &exclusiveGlobal))
+        return false;
+
+    // Iterate through the chain, looking for a same-origin object.
+    RootedObject head(cx, getExpandoChain(target));
+    while (head) {
+        if (expandoObjectMatchesConsumer(cx, head, origin, exclusiveGlobal)) {
+            expandoObject.set(head);
+            return true;
+        }
+        head = JS_GetReservedSlot(head, JSSLOT_EXPANDO_NEXT).toObjectOrNull();
+    }
+
+    // Not found.
+    return true;
+}
+
+bool
+XrayTraits::getExpandoObject(JSContext* cx, HandleObject target, HandleObject consumer,
+                             MutableHandleObject expandoObject)
+{
+    JSObject* consumerGlobal = js::GetGlobalForObjectCrossCompartment(consumer);
+    bool isSandbox = !strcmp(js::GetObjectJSClass(consumerGlobal)->name, "Sandbox");
+    return getExpandoObjectInternal(cx, target, ObjectPrincipal(consumer),
+                                    isSandbox ? consumerGlobal : nullptr,
+                                    expandoObject);
+}
+
+JSObject*
+XrayTraits::attachExpandoObject(JSContext* cx, HandleObject target,
+                                nsIPrincipal* origin, HandleObject exclusiveGlobal)
+{
+    // Make sure the compartments are sane.
+    MOZ_ASSERT(js::IsObjectInContextCompartment(target, cx));
+    MOZ_ASSERT(!exclusiveGlobal || js::IsObjectInContextCompartment(exclusiveGlobal, cx));
+
+    // No duplicates allowed.
+#ifdef DEBUG
+    {
+        RootedObject existingExpandoObject(cx);
+        if (getExpandoObjectInternal(cx, target, origin, exclusiveGlobal, &existingExpandoObject))
+            MOZ_ASSERT(!existingExpandoObject);
+        else
+            JS_ClearPendingException(cx);
+    }
+#endif
+
+    // Create the expando object.
+    const JSClass* expandoClass = getExpandoClass(cx, target);
+    MOZ_ASSERT(!strcmp(expandoClass->name, "XrayExpandoObject"));
+    RootedObject expandoObject(cx,
+      JS_NewObjectWithGivenProto(cx, expandoClass, nullptr));
+    if (!expandoObject)
+        return nullptr;
+
+    // AddRef and store the principal.
+    NS_ADDREF(origin);
+    JS_SetReservedSlot(expandoObject, JSSLOT_EXPANDO_ORIGIN, JS::PrivateValue(origin));
+
+    // Note the exclusive global, if any.
+    JS_SetReservedSlot(expandoObject, JSSLOT_EXPANDO_EXCLUSIVE_GLOBAL,
+                       ObjectOrNullValue(exclusiveGlobal));
+
+    // If this is our first expando object, take the opportunity to preserve
+    // the wrapper. This keeps our expandos alive even if the Xray wrapper gets
+    // collected.
+    RootedObject chain(cx, getExpandoChain(target));
+    if (!chain)
+        preserveWrapper(target);
+
+    // Insert it at the front of the chain.
+    JS_SetReservedSlot(expandoObject, JSSLOT_EXPANDO_NEXT, ObjectOrNullValue(chain));
+    setExpandoChain(cx, target, expandoObject);
+
+    return expandoObject;
+}
+
+JSObject*
+XrayTraits::ensureExpandoObject(JSContext* cx, HandleObject wrapper,
+                                HandleObject target)
+{
+    // Expando objects live in the target compartment.
+    JSAutoCompartment ac(cx, target);
+    RootedObject expandoObject(cx);
+    if (!getExpandoObject(cx, target, wrapper, &expandoObject))
+        return nullptr;
+    if (!expandoObject) {
+        // If the object is a sandbox, we don't want it to share expandos with
+        // anyone else, so we tag it with the sandbox global.
+        //
+        // NB: We first need to check the class, _then_ wrap for the target's
+        // compartment.
+        RootedObject consumerGlobal(cx, js::GetGlobalForObjectCrossCompartment(wrapper));
+        bool isSandbox = !strcmp(js::GetObjectJSClass(consumerGlobal)->name, "Sandbox");
+        if (!JS_WrapObject(cx, &consumerGlobal))
+            return nullptr;
+        expandoObject = attachExpandoObject(cx, target, ObjectPrincipal(wrapper),
+                                            isSandbox ? (HandleObject)consumerGlobal : nullptr);
+    }
+    return expandoObject;
+}
+
+bool
+XrayTraits::cloneExpandoChain(JSContext* cx, HandleObject dst, HandleObject src)
+{
+    MOZ_ASSERT(js::IsObjectInContextCompartment(dst, cx));
+    MOZ_ASSERT(getExpandoChain(dst) == nullptr);
+
+    RootedObject oldHead(cx, getExpandoChain(src));
+
+#ifdef DEBUG
+    // When this is called from dom::ReparentWrapper() there will be no native
+    // set for |dst|. Eventually it will be set to that of |src|.  This will
+    // prevent attachExpandoObject() from preserving the wrapper, but this is
+    // not a problem because in this case the wrapper will already have been
+    // preserved when expandos were originally added to |src|. Assert the
+    // wrapper for |src| has been preserved if it has expandos set.
+    if (oldHead) {
+        nsISupports* identity = mozilla::dom::UnwrapDOMObjectToISupports(src);
+        if (identity) {
+            nsWrapperCache* cache = nullptr;
+            CallQueryInterface(identity, &cache);
+            MOZ_ASSERT_IF(cache, cache->PreservingWrapper());
+        }
+    }
+#endif
+
+    while (oldHead) {
+        RootedObject exclusive(cx, JS_GetReservedSlot(oldHead,
+                                                      JSSLOT_EXPANDO_EXCLUSIVE_GLOBAL)
+                                                     .toObjectOrNull());
+        if (!JS_WrapObject(cx, &exclusive))
+            return false;
+        RootedObject newHead(cx, attachExpandoObject(cx, dst, GetExpandoObjectPrincipal(oldHead),
+                                                     exclusive));
+        if (!JS_CopyPropertiesFrom(cx, newHead, oldHead))
+            return false;
+        oldHead = JS_GetReservedSlot(oldHead, JSSLOT_EXPANDO_NEXT).toObjectOrNull();
+    }
+    return true;
+}
+
+void
+ClearXrayExpandoSlots(JSObject* target, size_t slotIndex)
+{
+    if (!NS_IsMainThread()) {
+        // No Xrays
+        return;
+    }
+
+    MOZ_ASSERT(GetXrayTraits(target) == &DOMXrayTraits::singleton);
+    RootingContext* rootingCx = RootingCx();
+    RootedObject rootedTarget(rootingCx, target);
+    RootedObject head(rootingCx,
+                      DOMXrayTraits::singleton.getExpandoChain(rootedTarget));
+    while (head) {
+        MOZ_ASSERT(JSCLASS_RESERVED_SLOTS(js::GetObjectClass(head)) > slotIndex);
+        js::SetReservedSlot(head, slotIndex, UndefinedValue());
+        head = js::GetReservedSlot(head, JSSLOT_EXPANDO_NEXT).toObjectOrNull();
+    }
+}
+
+JSObject*
+EnsureXrayExpandoObject(JSContext* cx, JS::HandleObject wrapper)
+{
+    MOZ_ASSERT(NS_IsMainThread());
+    MOZ_ASSERT(GetXrayTraits(wrapper) == &DOMXrayTraits::singleton);
+    MOZ_ASSERT(IsXrayWrapper(wrapper));
+
+    RootedObject target(cx, DOMXrayTraits::singleton.getTargetObject(wrapper));
+    return DOMXrayTraits::singleton.ensureExpandoObject(cx, wrapper, target);
+}
+
+const JSClass*
+XrayTraits::getExpandoClass(JSContext* cx, HandleObject target) const
+{
+    return &DefaultXrayExpandoObjectClass;
+}
+
+namespace XrayUtils {
+bool CloneExpandoChain(JSContext* cx, JSObject* dstArg, JSObject* srcArg)
+{
+    RootedObject dst(cx, dstArg);
+    RootedObject src(cx, srcArg);
+    return GetXrayTraits(src)->cloneExpandoChain(cx, dst, src);
+}
+} // namespace XrayUtils
+
+static JSObject*
+GetHolder(JSObject* obj)
+{
+    return &js::GetProxyExtra(obj, 0).toObject();
+}
+
+JSObject*
+XrayTraits::getHolder(JSObject* wrapper)
+{
+    MOZ_ASSERT(WrapperFactory::IsXrayWrapper(wrapper));
+    js::Value v = js::GetProxyExtra(wrapper, 0);
+    return v.isObject() ? &v.toObject() : nullptr;
+}
+
+JSObject*
+XrayTraits::ensureHolder(JSContext* cx, HandleObject wrapper)
+{
+    RootedObject holder(cx, getHolder(wrapper));
+    if (holder)
+        return holder;
+    holder = createHolder(cx, wrapper); // virtual trap.
+    if (holder)
+        js::SetProxyExtra(wrapper, 0, ObjectValue(*holder));
+    return holder;
+}
+
+namespace XrayUtils {
+
+bool
+IsXPCWNHolderClass(const JSClass* clasp)
+{
+  return clasp == &XPCWrappedNativeXrayTraits::HolderClass;
+}
+
+} // namespace XrayUtils
+
+static nsGlobalWindow*
+AsWindow(JSContext* cx, JSObject* wrapper)
+{
+  // We want to use our target object here, since we don't want to be
+  // doing a security check while unwrapping.
+  JSObject* target = XrayTraits::getTargetObject(wrapper);
+  return WindowOrNull(target);
+}
+
+static bool
+IsWindow(JSContext* cx, JSObject* wrapper)
+{
+    return !!AsWindow(cx, wrapper);
+}
+
+void
+XPCWrappedNativeXrayTraits::preserveWrapper(JSObject* target)
+{
+    XPCWrappedNative* wn = XPCWrappedNative::Get(target);
+    RefPtr<nsXPCClassInfo> ci;
+    CallQueryInterface(wn->Native(), getter_AddRefs(ci));
+    if (ci)
+        ci->PreserveWrapper(wn->Native());
+}
+
+static bool
+XrayToString(JSContext* cx, unsigned argc, JS::Value* vp);
+
+bool
+XPCWrappedNativeXrayTraits::resolveNativeProperty(JSContext* cx, HandleObject wrapper,
+                                                  HandleObject holder, HandleId id,
+                                                  MutableHandle<PropertyDescriptor> desc)
+{
+    MOZ_ASSERT(js::GetObjectJSClass(holder) == &HolderClass);
+
+    desc.object().set(nullptr);
+
+    // This will do verification and the method lookup for us.
+    RootedObject target(cx, getTargetObject(wrapper));
+    XPCCallContext ccx(cx, target, nullptr, id);
+
+    // There are no native numeric (or symbol-keyed) properties, so we can
+    // shortcut here. We will not find the property.
+    if (!JSID_IS_STRING(id))
+        return true;
+
+    XPCNativeInterface* iface;
+    XPCNativeMember* member;
+    XPCWrappedNative* wn = getWN(wrapper);
+
+    if (ccx.GetWrapper() != wn || !wn->IsValid()) {
+        return true;
+    }
+
+    if (!(iface = ccx.GetInterface()) || !(member = ccx.GetMember())) {
+        if (id != nsXPConnect::GetContextInstance()->GetStringID(XPCJSContext::IDX_TO_STRING))
+            return true;
+
+        JSFunction* toString = JS_NewFunction(cx, XrayToString, 0, 0, "toString");
+        if (!toString)
+            return false;
+
+        FillPropertyDescriptor(desc, wrapper, 0,
+                               ObjectValue(*JS_GetFunctionObject(toString)));
+
+        return JS_DefinePropertyById(cx, holder, id, desc) &&
+               JS_GetOwnPropertyDescriptorById(cx, holder, id, desc);
+    }
+
+    desc.object().set(holder);
+    desc.setAttributes(JSPROP_ENUMERATE);
+    desc.setGetter(nullptr);
+    desc.setSetter(nullptr);
+    desc.value().setUndefined();
+
+    RootedValue fval(cx, JS::UndefinedValue());
+    if (member->IsConstant()) {
+        if (!member->GetConstantValue(ccx, iface, desc.value().address())) {
+            JS_ReportErrorASCII(cx, "Failed to convert constant native property to JS value");
+            return false;
+        }
+    } else if (member->IsAttribute()) {
+        // This is a getter/setter. Clone a function for it.
+        if (!member->NewFunctionObject(ccx, iface, wrapper, fval.address())) {
+            JS_ReportErrorASCII(cx, "Failed to clone function object for native getter/setter");
+            return false;
+        }
+
+        unsigned attrs = desc.attributes();
+        attrs |= JSPROP_GETTER;
+        if (member->IsWritableAttribute())
+            attrs |= JSPROP_SETTER;
+
+        // Make the property shared on the holder so no slot is allocated
+        // for it. This avoids keeping garbage alive through that slot.
+        attrs |= JSPROP_SHARED;
+        desc.setAttributes(attrs);
+    } else {
+        // This is a method. Clone a function for it.
+        if (!member->NewFunctionObject(ccx, iface, wrapper, desc.value().address())) {
+            JS_ReportErrorASCII(cx, "Failed to clone function object for native function");
+            return false;
+        }
+
+        // Without a wrapper the function would live on the prototype. Since we
+        // don't have one, we have to avoid calling the scriptable helper's
+        // GetProperty method for this property, so null out the getter and
+        // setter here explicitly.
+        desc.setGetter(nullptr);
+        desc.setSetter(nullptr);
+    }
+
+    if (!JS_WrapValue(cx, desc.value()) || !JS_WrapValue(cx, &fval))
+        return false;
+
+    if (desc.hasGetterObject())
+        desc.setGetterObject(&fval.toObject());
+    if (desc.hasSetterObject())
+        desc.setSetterObject(&fval.toObject());
+
+    return JS_DefinePropertyById(cx, holder, id, desc);
+}
+
+static bool
+wrappedJSObject_getter(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+    if (!args.thisv().isObject()) {
+        JS_ReportErrorASCII(cx, "This value not an object");
+        return false;
+    }
+    RootedObject wrapper(cx, &args.thisv().toObject());
+    if (!IsWrapper(wrapper) || !WrapperFactory::IsXrayWrapper(wrapper) ||
+        !WrapperFactory::AllowWaiver(wrapper)) {
+        JS_ReportErrorASCII(cx, "Unexpected object");
+        return false;
+    }
+
+    args.rval().setObject(*wrapper);
+
+    return WrapperFactory::WaiveXrayAndWrap(cx, args.rval());
+}
+
+bool
+XrayTraits::resolveOwnProperty(JSContext* cx, const Wrapper& jsWrapper,
+                               HandleObject wrapper, HandleObject holder, HandleId id,
+                               MutableHandle<PropertyDescriptor> desc)
+{
+    desc.object().set(nullptr);
+    RootedObject target(cx, getTargetObject(wrapper));
+    RootedObject expando(cx);
+    if (!getExpandoObject(cx, target, wrapper, &expando))
+        return false;
+
+    // Check for expando properties first. Note that the expando object lives
+    // in the target compartment.
+    bool found = false;
+    if (expando) {
+        JSAutoCompartment ac(cx, expando);
+        if (!JS_GetOwnPropertyDescriptorById(cx, expando, id, desc))
+            return false;
+        found = !!desc.object();
+    }
+
+    // Next, check for ES builtins.
+    if (!found && JS_IsGlobalObject(target)) {
+        JSProtoKey key = JS_IdToProtoKey(cx, id);
+        JSAutoCompartment ac(cx, target);
+        if (key != JSProto_Null) {
+            MOZ_ASSERT(key < JSProto_LIMIT);
+            RootedObject constructor(cx);
+            if (!JS_GetClassObject(cx, key, &constructor))
+                return false;
+            MOZ_ASSERT(constructor);
+            desc.value().set(ObjectValue(*constructor));
+            found = true;
+        } else if (id == GetJSIDByIndex(cx, XPCJSContext::IDX_EVAL)) {
+            RootedObject eval(cx);
+            if (!js::GetOriginalEval(cx, target, &eval))
+                return false;
+            desc.value().set(ObjectValue(*eval));
+            found = true;
+        }
+    }
+
+    if (found) {
+        if (!JS_WrapPropertyDescriptor(cx, desc))
+            return false;
+        // Pretend the property lives on the wrapper.
+        desc.object().set(wrapper);
+        return true;
+    }
+
+    // Handle .wrappedJSObject for subsuming callers. This should move once we
+    // sort out own-ness for the holder.
+    if (id == GetJSIDByIndex(cx, XPCJSContext::IDX_WRAPPED_JSOBJECT) &&
+        WrapperFactory::AllowWaiver(wrapper))
+    {
+        if (!JS_AlreadyHasOwnPropertyById(cx, holder, id, &found))
+            return false;
+        if (!found && !JS_DefinePropertyById(cx, holder, id, UndefinedHandleValue,
+                                             JSPROP_ENUMERATE | JSPROP_SHARED,
+                                             wrappedJSObject_getter)) {
+            return false;
+        }
+        if (!JS_GetOwnPropertyDescriptorById(cx, holder, id, desc))
+            return false;
+        desc.object().set(wrapper);
+        return true;
+    }
+
+    return true;
+}
+
+bool
+XPCWrappedNativeXrayTraits::resolveOwnProperty(JSContext* cx, const Wrapper& jsWrapper,
+                                               HandleObject wrapper, HandleObject holder,
+                                               HandleId id,
+                                               MutableHandle<PropertyDescriptor> desc)
+{
+    // Call the common code.
+    bool ok = XrayTraits::resolveOwnProperty(cx, jsWrapper, wrapper, holder,
+                                             id, desc);
+    if (!ok || desc.object())
+        return ok;
+
+    // Xray wrappers don't use the regular wrapper hierarchy, so we should be
+    // in the wrapper's compartment here, not the wrappee.
+    MOZ_ASSERT(js::IsObjectInContextCompartment(wrapper, cx));
+
+    return JS_GetOwnPropertyDescriptorById(cx, holder, id, desc);
+}
+
+bool
+XPCWrappedNativeXrayTraits::enumerateNames(JSContext* cx, HandleObject wrapper, unsigned flags,
+                                           AutoIdVector& props)
+{
+    // Force all native properties to be materialized onto the wrapped native.
+    AutoIdVector wnProps(cx);
+    {
+        RootedObject target(cx, singleton.getTargetObject(wrapper));
+        JSAutoCompartment ac(cx, target);
+        if (!js::GetPropertyKeys(cx, target, flags, &wnProps))
+            return false;
+    }
+
+    // Go through the properties we found on the underlying object and see if
+    // they appear on the XrayWrapper. If it throws (which may happen if the
+    // wrapper is a SecurityWrapper), just clear the exception and move on.
+    MOZ_ASSERT(!JS_IsExceptionPending(cx));
+    if (!props.reserve(wnProps.length()))
+        return false;
+    for (size_t n = 0; n < wnProps.length(); ++n) {
+        RootedId id(cx, wnProps[n]);
+        bool hasProp;
+        if (JS_HasPropertyById(cx, wrapper, id, &hasProp) && hasProp)
+            props.infallibleAppend(id);
+        JS_ClearPendingException(cx);
+    }
+    return true;
+}
+
+JSObject*
+XPCWrappedNativeXrayTraits::createHolder(JSContext* cx, JSObject* wrapper)
+{
+    return JS_NewObjectWithGivenProto(cx, &HolderClass, nullptr);
+}
+
+bool
+XPCWrappedNativeXrayTraits::call(JSContext* cx, HandleObject wrapper,
+                                 const JS::CallArgs& args,
+                                 const js::Wrapper& baseInstance)
+{
+    // Run the call hook of the wrapped native.
+    XPCWrappedNative* wn = getWN(wrapper);
+    if (NATIVE_HAS_FLAG(wn, WantCall)) {
+        XPCCallContext ccx(cx, wrapper, nullptr, JSID_VOIDHANDLE, args.length(),
+                           args.array(), args.rval().address());
+        if (!ccx.IsValid())
+            return false;
+        bool ok = true;
+        nsresult rv = wn->GetScriptableInfo()->GetCallback()->Call(
+            wn, cx, wrapper, args, &ok);
+        if (NS_FAILED(rv)) {
+            if (ok)
+                XPCThrower::Throw(rv, cx);
+            return false;
+        }
+    }
+
+    return true;
+
+}
+
+bool
+XPCWrappedNativeXrayTraits::construct(JSContext* cx, HandleObject wrapper,
+                                      const JS::CallArgs& args,
+                                      const js::Wrapper& baseInstance)
+{
+    // Run the construct hook of the wrapped native.
+    XPCWrappedNative* wn = getWN(wrapper);
+    if (NATIVE_HAS_FLAG(wn, WantConstruct)) {
+        XPCCallContext ccx(cx, wrapper, nullptr, JSID_VOIDHANDLE, args.length(),
+                           args.array(), args.rval().address());
+        if (!ccx.IsValid())
+            return false;
+        bool ok = true;
+        nsresult rv = wn->GetScriptableInfo()->GetCallback()->Construct(
+            wn, cx, wrapper, args, &ok);
+        if (NS_FAILED(rv)) {
+            if (ok)
+                XPCThrower::Throw(rv, cx);
+            return false;
+        }
+    }
+
+    return true;
+
+}
+
+bool
+DOMXrayTraits::resolveOwnProperty(JSContext* cx, const Wrapper& jsWrapper, HandleObject wrapper,
+                                  HandleObject holder, HandleId id,
+                                  MutableHandle<PropertyDescriptor> desc)
+{
+    // Call the common code.
+    bool ok = XrayTraits::resolveOwnProperty(cx, jsWrapper, wrapper, holder, id, desc);
+    if (!ok || desc.object())
+        return ok;
+
+    // Check for indexed access on a window.
+    uint32_t index = GetArrayIndexFromId(cx, id);
+    if (IsArrayIndex(index)) {
+        nsGlobalWindow* win = AsWindow(cx, wrapper);
+        // Note: As() unwraps outer windows to get to the inner window.
+        if (win) {
+            nsCOMPtr<nsPIDOMWindowOuter> subframe = win->IndexedGetter(index);
+            if (subframe) {
+                subframe->EnsureInnerWindow();
+                nsGlobalWindow* global = nsGlobalWindow::Cast(subframe);
+                JSObject* obj = global->FastGetGlobalJSObject();
+                if (MOZ_UNLIKELY(!obj)) {
+                    // It's gone?
+                    return xpc::Throw(cx, NS_ERROR_FAILURE);
+                }
+                ExposeObjectToActiveJS(obj);
+                desc.value().setObject(*obj);
+                FillPropertyDescriptor(desc, wrapper, true);
+                return JS_WrapPropertyDescriptor(cx, desc);
+            }
+        }
+    }
+
+    if (!JS_GetOwnPropertyDescriptorById(cx, holder, id, desc))
+        return false;
+    if (desc.object()) {
+        desc.object().set(wrapper);
+        return true;
+    }
+
+    RootedObject obj(cx, getTargetObject(wrapper));
+    bool cacheOnHolder;
+    if (!XrayResolveOwnProperty(cx, wrapper, obj, id, desc, cacheOnHolder))
+        return false;
+
+    MOZ_ASSERT(!desc.object() || desc.object() == wrapper, "What did we resolve this on?");
+
+    if (!desc.object() || !cacheOnHolder)
+        return true;
+
+    return JS_DefinePropertyById(cx, holder, id, desc) &&
+           JS_GetOwnPropertyDescriptorById(cx, holder, id, desc);
+}
+
+bool
+DOMXrayTraits::delete_(JSContext* cx, JS::HandleObject wrapper,
+                       JS::HandleId id, JS::ObjectOpResult& result)
+{
+    RootedObject target(cx, getTargetObject(wrapper));
+    return XrayDeleteNamedProperty(cx, wrapper, target, id, result);
+}
+
+bool
+DOMXrayTraits::defineProperty(JSContext* cx, HandleObject wrapper, HandleId id,
+                              Handle<PropertyDescriptor> desc,
+                              Handle<PropertyDescriptor> existingDesc,
+                              JS::ObjectOpResult& result, bool* defined)
+{
+    // Check for an indexed property on a Window.  If that's happening, do
+    // nothing but claim we defined it so it won't get added as an expando.
+    if (IsWindow(cx, wrapper)) {
+        if (IsArrayIndex(GetArrayIndexFromId(cx, id))) {
+            *defined = true;
+            return result.succeed();
+        }
+    }
+
+    JS::Rooted<JSObject*> obj(cx, getTargetObject(wrapper));
+    return XrayDefineProperty(cx, wrapper, obj, id, desc, result, defined);
+}
+
+bool
+DOMXrayTraits::enumerateNames(JSContext* cx, HandleObject wrapper, unsigned flags,
+                              AutoIdVector& props)
+{
+    JS::Rooted<JSObject*> obj(cx, getTargetObject(wrapper));
+    return XrayOwnPropertyKeys(cx, wrapper, obj, flags, props);
+}
+
+bool
+DOMXrayTraits::call(JSContext* cx, HandleObject wrapper,
+                    const JS::CallArgs& args, const js::Wrapper& baseInstance)
+{
+    RootedObject obj(cx, getTargetObject(wrapper));
+    const js::Class* clasp = js::GetObjectClass(obj);
+    // What we have is either a WebIDL interface object, a WebIDL prototype
+    // object, or a WebIDL instance object.  WebIDL prototype objects never have
+    // a clasp->call.  WebIDL interface objects we want to invoke on the xray
+    // compartment.  WebIDL instance objects either don't have a clasp->call or
+    // are using "legacycaller", which basically means plug-ins.  We want to
+    // call those on the content compartment.
+    if (clasp->flags & JSCLASS_IS_DOMIFACEANDPROTOJSCLASS) {
+        if (JSNative call = clasp->getCall()) {
+            // call it on the Xray compartment
+            if (!call(cx, args.length(), args.base()))
+                return false;
+        } else {
+            RootedValue v(cx, ObjectValue(*wrapper));
+            js::ReportIsNotFunction(cx, v);
+            return false;
+        }
+    } else {
+        // This is only reached for WebIDL instance objects, and in practice
+        // only for plugins.  Just call them on the content compartment.
+        if (!baseInstance.call(cx, wrapper, args))
+            return false;
+    }
+    return JS_WrapValue(cx, args.rval());
+}
+
+bool
+DOMXrayTraits::construct(JSContext* cx, HandleObject wrapper,
+                         const JS::CallArgs& args, const js::Wrapper& baseInstance)
+{
+    RootedObject obj(cx, getTargetObject(wrapper));
+    MOZ_ASSERT(mozilla::dom::HasConstructor(obj));
+    const js::Class* clasp = js::GetObjectClass(obj);
+    // See comments in DOMXrayTraits::call() explaining what's going on here.
+    if (clasp->flags & JSCLASS_IS_DOMIFACEANDPROTOJSCLASS) {
+        if (JSNative construct = clasp->getConstruct()) {
+            if (!construct(cx, args.length(), args.base()))
+                return false;
+        } else {
+            RootedValue v(cx, ObjectValue(*wrapper));
+            js::ReportIsNotFunction(cx, v);
+            return false;
+        }
+    } else {
+        if (!baseInstance.construct(cx, wrapper, args))
+            return false;
+    }
+    if (!args.rval().isObject() || !JS_WrapValue(cx, args.rval()))
+        return false;
+    return true;
+}
+
+bool
+DOMXrayTraits::getPrototype(JSContext* cx, JS::HandleObject wrapper,
+                            JS::HandleObject target,
+                            JS::MutableHandleObject protop)
+{
+    return mozilla::dom::XrayGetNativeProto(cx, target, protop);
+}
+
+void
+DOMXrayTraits::preserveWrapper(JSObject* target)
+{
+    nsISupports* identity = mozilla::dom::UnwrapDOMObjectToISupports(target);
+    if (!identity)
+        return;
+    nsWrapperCache* cache = nullptr;
+    CallQueryInterface(identity, &cache);
+    if (cache)
+        cache->PreserveWrapper(identity);
+}
+
+JSObject*
+DOMXrayTraits::createHolder(JSContext* cx, JSObject* wrapper)
+{
+    return JS_NewObjectWithGivenProto(cx, nullptr, nullptr);
+}
+
+const JSClass*
+DOMXrayTraits::getExpandoClass(JSContext* cx, HandleObject target) const
+{
+    return XrayGetExpandoClass(cx, target);
+}
+
+namespace XrayUtils {
+
+JSObject*
+GetNativePropertiesObject(JSContext* cx, JSObject* wrapper)
+{
+    MOZ_ASSERT(js::IsWrapper(wrapper) && WrapperFactory::IsXrayWrapper(wrapper),
+               "bad object passed in");
+
+    JSObject* holder = GetHolder(wrapper);
+    MOZ_ASSERT(holder, "uninitialized wrapper being used?");
+    return holder;
+}
+
+bool
+HasNativeProperty(JSContext* cx, HandleObject wrapper, HandleId id, bool* hasProp)
+{
+    MOZ_ASSERT(WrapperFactory::IsXrayWrapper(wrapper));
+    XrayTraits* traits = GetXrayTraits(wrapper);
+    MOZ_ASSERT(traits);
+    RootedObject holder(cx, traits->ensureHolder(cx, wrapper));
+    NS_ENSURE_TRUE(holder, false);
+    *hasProp = false;
+    Rooted<PropertyDescriptor> desc(cx);
+    const Wrapper* handler = Wrapper::wrapperHandler(wrapper);
+
+    // Try resolveOwnProperty.
+    if (!traits->resolveOwnProperty(cx, *handler, wrapper, holder, id, &desc))
+        return false;
+    if (desc.object()) {
+        *hasProp = true;
+        return true;
+    }
+
+    // Try the holder.
+    bool found = false;
+    if (!JS_AlreadyHasOwnPropertyById(cx, holder, id, &found))
+        return false;
+    if (found) {
+        *hasProp = true;
+        return true;
+    }
+
+    // Try resolveNativeProperty.
+    if (!traits->resolveNativeProperty(cx, wrapper, holder, id, &desc))
+        return false;
+    *hasProp = !!desc.object();
+    return true;
+}
+
+} // namespace XrayUtils
+
+static bool
+XrayToString(JSContext* cx, unsigned argc, Value* vp)
+{
+    CallArgs args = CallArgsFromVp(argc, vp);
+
+    if (!args.thisv().isObject()) {
+        JS_ReportErrorASCII(cx, "XrayToString called on an incompatible object");
+        return false;
+    }
+
+    RootedObject wrapper(cx, &args.thisv().toObject());
+    if (!wrapper)
+        return false;
+    if (IsWrapper(wrapper) &&
+        GetProxyHandler(wrapper) == &sandboxCallableProxyHandler) {
+        wrapper = xpc::SandboxCallableProxyHandler::wrappedObject(wrapper);
+    }
+    if (!IsWrapper(wrapper) || !WrapperFactory::IsXrayWrapper(wrapper)) {
+        JS_ReportErrorASCII(cx, "XrayToString called on an incompatible object");
+        return false;
+    }
+
+    RootedObject obj(cx, XrayTraits::getTargetObject(wrapper));
+    if (GetXrayType(obj) != XrayForWrappedNative) {
+        JS_ReportErrorASCII(cx, "XrayToString called on an incompatible object");
+        return false;
+    }
+
+    static const char start[] = "[object XrayWrapper ";
+    static const char end[] = "]";
+    nsAutoString result;
+    result.AppendASCII(start);
+
+    XPCCallContext ccx(cx, obj);
+    XPCWrappedNative* wn = XPCWrappedNativeXrayTraits::getWN(wrapper);
+    char* wrapperStr = wn->ToString();
+    if (!wrapperStr) {
+        JS_ReportOutOfMemory(cx);
+        return false;
+    }
+    result.AppendASCII(wrapperStr);
+    JS_smprintf_free(wrapperStr);
+
+    result.AppendASCII(end);
+
+    JSString* str = JS_NewUCStringCopyN(cx, result.get(), result.Length());
+    if (!str)
+        return false;
+
+    args.rval().setString(str);
+    return true;
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::preventExtensions(JSContext* cx, HandleObject wrapper,
+                                             ObjectOpResult& result) const
+{
+    // Xray wrappers are supposed to provide a clean view of the target
+    // reflector, hiding any modifications by script in the target scope.  So
+    // even if that script freezes the reflector, we don't want to make that
+    // visible to the caller. DOM reflectors are always extensible by default,
+    // so we can just return failure here.
+    return result.failCantPreventExtensions();
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::isExtensible(JSContext* cx, JS::Handle<JSObject*> wrapper,
+                                        bool* extensible) const
+{
+    // See above.
+    *extensible = true;
+    return true;
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::getPropertyDescriptor(JSContext* cx, HandleObject wrapper, HandleId id,
+                                                 JS::MutableHandle<PropertyDescriptor> desc)
+                                                 const
+{
+    assertEnteredPolicy(cx, wrapper, id, BaseProxyHandler::GET | BaseProxyHandler::SET |
+                                         BaseProxyHandler::GET_PROPERTY_DESCRIPTOR);
+    RootedObject holder(cx, Traits::singleton.ensureHolder(cx, wrapper));
+
+    if (!holder)
+        return false;
+
+    // Ordering is important here.
+    //
+    // We first need to call resolveOwnProperty, even before checking the holder,
+    // because there might be a new dynamic |own| property that appears and
+    // shadows a previously-resolved non-own property that we cached on the
+    // holder. This can happen with indexed properties on NodeLists, for example,
+    // which are |own| value props.
+    //
+    // resolveOwnProperty may or may not cache what it finds on the holder,
+    // depending on how ephemeral it decides the property is. XPCWN |own|
+    // properties generally end up on the holder via Resolve, whereas
+    // NodeList |own| properties don't get defined on the holder, since they're
+    // supposed to be dynamic. This means that we have to first check the result
+    // of resolveOwnProperty, and _then_, if that comes up blank, check the
+    // holder for any cached native properties.
+    //
+    // Finally, we call resolveNativeProperty, which checks non-own properties,
+    // and unconditionally caches what it finds on the holder.
+
+    // Check resolveOwnProperty.
+    if (!Traits::singleton.resolveOwnProperty(cx, *this, wrapper, holder, id, desc))
+        return false;
+
+    // Check the holder.
+    if (!desc.object() && !JS_GetOwnPropertyDescriptorById(cx, holder, id, desc))
+        return false;
+    if (desc.object()) {
+        desc.object().set(wrapper);
+        return true;
+    }
+
+    // Nothing in the cache. Call through, and cache the result.
+    if (!Traits::singleton.resolveNativeProperty(cx, wrapper, holder, id, desc))
+        return false;
+
+    // We need to handle named access on the Window somewhere other than
+    // Traits::resolveOwnProperty, because per spec it happens on the Global
+    // Scope Polluter and thus the resulting properties are non-|own|. However,
+    // we're set up (above) to cache (on the holder) anything that comes out of
+    // resolveNativeProperty, which we don't want for something dynamic like
+    // named access. So we just handle it separately here.
+    nsGlobalWindow* win = nullptr;
+    if (!desc.object() &&
+        JSID_IS_STRING(id) &&
+        (win = AsWindow(cx, wrapper)))
+    {
+        nsAutoJSString name;
+        if (!name.init(cx, JSID_TO_STRING(id)))
+            return false;
+        if (nsCOMPtr<nsPIDOMWindowOuter> childDOMWin = win->GetChildWindow(name)) {
+            auto* cwin = nsGlobalWindow::Cast(childDOMWin);
+            JSObject* childObj = cwin->FastGetGlobalJSObject();
+            if (MOZ_UNLIKELY(!childObj))
+                return xpc::Throw(cx, NS_ERROR_FAILURE);
+            ExposeObjectToActiveJS(childObj);
+            FillPropertyDescriptor(desc, wrapper, ObjectValue(*childObj),
+                                   /* readOnly = */ true);
+            return JS_WrapPropertyDescriptor(cx, desc);
+        }
+    }
+
+    // If we still have nothing, we're done.
+    if (!desc.object())
+        return true;
+
+    if (!JS_DefinePropertyById(cx, holder, id, desc) ||
+        !JS_GetOwnPropertyDescriptorById(cx, holder, id, desc))
+    {
+        return false;
+    }
+    MOZ_ASSERT(desc.object());
+    desc.object().set(wrapper);
+    return true;
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::getOwnPropertyDescriptor(JSContext* cx, HandleObject wrapper, HandleId id,
+                                                    JS::MutableHandle<PropertyDescriptor> desc)
+                                                    const
+{
+    assertEnteredPolicy(cx, wrapper, id, BaseProxyHandler::GET | BaseProxyHandler::SET |
+                                         BaseProxyHandler::GET_PROPERTY_DESCRIPTOR);
+    RootedObject holder(cx, Traits::singleton.ensureHolder(cx, wrapper));
+
+    if (!Traits::singleton.resolveOwnProperty(cx, *this, wrapper, holder, id, desc))
+        return false;
+    if (desc.object())
+        desc.object().set(wrapper);
+    return true;
+}
+
+// Consider what happens when chrome does |xray.expando = xray.wrappedJSObject|.
+//
+// Since the expando comes from the target compartment, wrapping it back into
+// the target compartment to define it on the expando object ends up stripping
+// off the Xray waiver that gives |xray| and |xray.wrappedJSObject| different
+// identities. This is generally the right thing to do when wrapping across
+// compartments, but is incorrect in the special case of the Xray expando
+// object. Manually re-apply Xrays if necessary.
+//
+// NB: In order to satisfy the invariants of WaiveXray, we need to pass
+// in an object sans security wrapper, which means we need to strip off any
+// potential same-compartment security wrapper that may have been applied
+// to the content object. This is ok, because the the expando object is only
+// ever accessed by code across the compartment boundary.
+static bool
+RecreateLostWaivers(JSContext* cx, const PropertyDescriptor* orig,
+                    MutableHandle<PropertyDescriptor> wrapped)
+{
+    // Compute whether the original objects were waived, and implicitly, whether
+    // they were objects at all.
+    bool valueWasWaived =
+        orig->value.isObject() &&
+        WrapperFactory::HasWaiveXrayFlag(&orig->value.toObject());
+    bool getterWasWaived =
+        (orig->attrs & JSPROP_GETTER) && orig->getter &&
+        WrapperFactory::HasWaiveXrayFlag(JS_FUNC_TO_DATA_PTR(JSObject*, orig->getter));
+    bool setterWasWaived =
+        (orig->attrs & JSPROP_SETTER) && orig->setter &&
+        WrapperFactory::HasWaiveXrayFlag(JS_FUNC_TO_DATA_PTR(JSObject*, orig->setter));
+
+    // Recreate waivers. Note that for value, we need an extra UncheckedUnwrap
+    // to handle same-compartment security wrappers (see above). This should
+    // never happen for getters/setters.
+
+    RootedObject rewaived(cx);
+    if (valueWasWaived && !IsCrossCompartmentWrapper(&wrapped.value().toObject())) {
+        rewaived = &wrapped.value().toObject();
+        rewaived = WrapperFactory::WaiveXray(cx, UncheckedUnwrap(rewaived));
+        NS_ENSURE_TRUE(rewaived, false);
+        wrapped.value().set(ObjectValue(*rewaived));
+    }
+    if (getterWasWaived && !IsCrossCompartmentWrapper(wrapped.getterObject())) {
+        MOZ_ASSERT(CheckedUnwrap(wrapped.getterObject()));
+        rewaived = WrapperFactory::WaiveXray(cx, wrapped.getterObject());
+        NS_ENSURE_TRUE(rewaived, false);
+        wrapped.setGetterObject(rewaived);
+    }
+    if (setterWasWaived && !IsCrossCompartmentWrapper(wrapped.setterObject())) {
+        MOZ_ASSERT(CheckedUnwrap(wrapped.setterObject()));
+        rewaived = WrapperFactory::WaiveXray(cx, wrapped.setterObject());
+        NS_ENSURE_TRUE(rewaived, false);
+        wrapped.setSetterObject(rewaived);
+    }
+
+    return true;
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::defineProperty(JSContext* cx, HandleObject wrapper,
+                                          HandleId id, Handle<PropertyDescriptor> desc,
+                                          ObjectOpResult& result) const
+{
+    assertEnteredPolicy(cx, wrapper, id, BaseProxyHandler::SET);
+
+    Rooted<PropertyDescriptor> existing_desc(cx);
+    if (!JS_GetPropertyDescriptorById(cx, wrapper, id, &existing_desc))
+        return false;
+
+    // Note that the check here is intended to differentiate between own and
+    // non-own properties, since the above lookup is not limited to own
+    // properties. At present, this may not always do the right thing because
+    // we often lie (sloppily) about where we found properties and set
+    // desc.object() to |wrapper|. Once we fully fix our Xray prototype semantics,
+    // this should work as intended.
+    if (existing_desc.object() == wrapper && !existing_desc.configurable()) {
+        // We have a non-configurable property. See if the caller is trying to
+        // re-configure it in any way other than making it non-writable.
+        if (existing_desc.isAccessorDescriptor() || desc.isAccessorDescriptor() ||
+            (desc.hasEnumerable() && existing_desc.enumerable() != desc.enumerable()) ||
+            (desc.hasWritable() && !existing_desc.writable() && desc.writable()))
+        {
+            // We should technically report non-configurability in strict mode, but
+            // doing that via JSAPI used to be a lot of trouble. See bug 1135997.
+            return result.succeed();
+        }
+        if (!existing_desc.writable()) {
+            // Same as the above for non-writability.
+            return result.succeed();
+        }
+    }
+
+    bool defined = false;
+    if (!Traits::singleton.defineProperty(cx, wrapper, id, desc, existing_desc, result, &defined))
+        return false;
+    if (defined)
+        return true;
+
+    // We're placing an expando. The expando objects live in the target
+    // compartment, so we need to enter it.
+    RootedObject target(cx, Traits::singleton.getTargetObject(wrapper));
+    JSAutoCompartment ac(cx, target);
+
+    // Grab the relevant expando object.
+    RootedObject expandoObject(cx, Traits::singleton.ensureExpandoObject(cx, wrapper,
+                                                                         target));
+    if (!expandoObject)
+        return false;
+
+    // Wrap the property descriptor for the target compartment.
+    Rooted<PropertyDescriptor> wrappedDesc(cx, desc);
+    if (!JS_WrapPropertyDescriptor(cx, &wrappedDesc))
+        return false;
+
+    // Fix up Xray waivers.
+    if (!RecreateLostWaivers(cx, desc.address(), &wrappedDesc))
+        return false;
+
+    return JS_DefinePropertyById(cx, expandoObject, id, wrappedDesc, result);
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::ownPropertyKeys(JSContext* cx, HandleObject wrapper,
+                                           AutoIdVector& props) const
+{
+    assertEnteredPolicy(cx, wrapper, JSID_VOID, BaseProxyHandler::ENUMERATE);
+    return getPropertyKeys(cx, wrapper, JSITER_OWNONLY | JSITER_HIDDEN | JSITER_SYMBOLS, props);
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::delete_(JSContext* cx, HandleObject wrapper,
+                                   HandleId id, ObjectOpResult& result) const
+{
+    assertEnteredPolicy(cx, wrapper, id, BaseProxyHandler::SET);
+
+    // Check the expando object.
+    RootedObject target(cx, Traits::getTargetObject(wrapper));
+    RootedObject expando(cx);
+    if (!Traits::singleton.getExpandoObject(cx, target, wrapper, &expando))
+        return false;
+
+    if (expando) {
+        JSAutoCompartment ac(cx, expando);
+        bool hasProp;
+        if (!JS_HasPropertyById(cx, expando, id, &hasProp)) {
+            return false;
+        }
+        if (hasProp) {
+            return JS_DeletePropertyById(cx, expando, id, result);
+        }
+    }
+
+    return Traits::singleton.delete_(cx, wrapper, id, result);
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::get(JSContext* cx, HandleObject wrapper,
+                               HandleValue receiver, HandleId id,
+                               MutableHandleValue vp) const
+{
+    // Skip our Base if it isn't already ProxyHandler.
+    // NB: None of the functions we call are prepared for the receiver not
+    // being the wrapper, so ignore the receiver here.
+    RootedValue thisv(cx);
+    if (Traits::HasPrototype)
+      thisv = receiver;
+    else
+      thisv.setObject(*wrapper);
+
+    // This uses getPropertyDescriptor for backward compatibility with
+    // the old BaseProxyHandler::get implementation.
+    Rooted<PropertyDescriptor> desc(cx);
+    if (!getPropertyDescriptor(cx, wrapper, id, &desc))
+        return false;
+    desc.assertCompleteIfFound();
+
+    if (!desc.object()) {
+        vp.setUndefined();
+        return true;
+    }
+
+    // Everything after here follows [[Get]] for ordinary objects.
+    if (desc.isDataDescriptor()) {
+        vp.set(desc.value());
+        return true;
+    }
+
+    MOZ_ASSERT(desc.isAccessorDescriptor());
+    RootedObject getter(cx, desc.getterObject());
+
+    if (!getter) {
+        vp.setUndefined();
+        return true;
+    }
+
+    return Call(cx, thisv, getter, HandleValueArray::empty(), vp);
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::set(JSContext* cx, HandleObject wrapper, HandleId id, HandleValue v,
+                               HandleValue receiver, ObjectOpResult& result) const
+{
+    MOZ_ASSERT(!Traits::HasPrototype);
+    // Skip our Base if it isn't already BaseProxyHandler.
+    // NB: None of the functions we call are prepared for the receiver not
+    // being the wrapper, so ignore the receiver here.
+    RootedValue wrapperValue(cx, ObjectValue(*wrapper));
+    return js::BaseProxyHandler::set(cx, wrapper, id, v, wrapperValue, result);
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::has(JSContext* cx, HandleObject wrapper,
+                               HandleId id, bool* bp) const
+{
+    // This uses getPropertyDescriptor for backward compatibility with
+    // the old BaseProxyHandler::has implementation.
+    Rooted<PropertyDescriptor> desc(cx);
+    if (!getPropertyDescriptor(cx, wrapper, id, &desc))
+        return false;
+
+    *bp = !!desc.object();
+    return true;
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::hasOwn(JSContext* cx, HandleObject wrapper,
+                                  HandleId id, bool* bp) const
+{
+    // Skip our Base if it isn't already ProxyHandler.
+    return js::BaseProxyHandler::hasOwn(cx, wrapper, id, bp);
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::getOwnEnumerablePropertyKeys(JSContext* cx,
+                                                        HandleObject wrapper,
+                                                        AutoIdVector& props) const
+{
+    // Skip our Base if it isn't already ProxyHandler.
+    return js::BaseProxyHandler::getOwnEnumerablePropertyKeys(cx, wrapper, props);
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::enumerate(JSContext* cx, HandleObject wrapper,
+                                     MutableHandleObject objp) const
+{
+    // Skip our Base if it isn't already ProxyHandler.
+    return js::BaseProxyHandler::enumerate(cx, wrapper, objp);
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::call(JSContext* cx, HandleObject wrapper, const JS::CallArgs& args) const
+{
+    assertEnteredPolicy(cx, wrapper, JSID_VOID, BaseProxyHandler::CALL);
+    // Hard cast the singleton since SecurityWrapper doesn't have one.
+    return Traits::call(cx, wrapper, args, Base::singleton);
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::construct(JSContext* cx, HandleObject wrapper, const JS::CallArgs& args) const
+{
+    assertEnteredPolicy(cx, wrapper, JSID_VOID, BaseProxyHandler::CALL);
+    // Hard cast the singleton since SecurityWrapper doesn't have one.
+    return Traits::construct(cx, wrapper, args, Base::singleton);
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::getBuiltinClass(JSContext* cx, JS::HandleObject wrapper, js::ESClass* cls) const
+{
+    return Traits::getBuiltinClass(cx, wrapper, Base::singleton, cls);
+}
+
+template <typename Base, typename Traits>
+const char*
+XrayWrapper<Base, Traits>::className(JSContext* cx, HandleObject wrapper) const
+{
+    return Traits::className(cx, wrapper, Base::singleton);
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::getPrototype(JSContext* cx, JS::HandleObject wrapper,
+                                        JS::MutableHandleObject protop) const
+{
+    // We really only want this override for non-SecurityWrapper-inheriting
+    // |Base|. But doing that statically with templates requires partial method
+    // specializations (and therefore a helper class), which is all more trouble
+    // than it's worth. Do a dynamic check.
+    if (Base::hasSecurityPolicy())
+        return Base::getPrototype(cx, wrapper, protop);
+
+    RootedObject target(cx, Traits::getTargetObject(wrapper));
+    RootedObject expando(cx);
+    if (!Traits::singleton.getExpandoObject(cx, target, wrapper, &expando))
+        return false;
+
+    // We want to keep the Xray's prototype distinct from that of content, but
+    // only if there's been a set. If there's not an expando, or the expando
+    // slot is |undefined|, hand back the default proto, appropriately wrapped.
+
+    RootedValue v(cx);
+    if (expando) {
+        JSAutoCompartment ac(cx, expando);
+        v = JS_GetReservedSlot(expando, JSSLOT_EXPANDO_PROTOTYPE);
+    }
+    if (v.isUndefined())
+        return getPrototypeHelper(cx, wrapper, target, protop);
+
+    protop.set(v.toObjectOrNull());
+    return JS_WrapObject(cx, protop);
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::setPrototype(JSContext* cx, JS::HandleObject wrapper,
+                                        JS::HandleObject proto, JS::ObjectOpResult& result) const
+{
+    // Do this only for non-SecurityWrapper-inheriting |Base|. See the comment
+    // in getPrototype().
+    if (Base::hasSecurityPolicy())
+        return Base::setPrototype(cx, wrapper, proto, result);
+
+    RootedObject target(cx, Traits::getTargetObject(wrapper));
+    RootedObject expando(cx, Traits::singleton.ensureExpandoObject(cx, wrapper, target));
+    if (!expando)
+        return false;
+
+    // The expando lives in the target's compartment, so do our installation there.
+    JSAutoCompartment ac(cx, target);
+
+    RootedValue v(cx, ObjectOrNullValue(proto));
+    if (!JS_WrapValue(cx, &v))
+        return false;
+    JS_SetReservedSlot(expando, JSSLOT_EXPANDO_PROTOTYPE, v);
+    return result.succeed();
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::getPrototypeIfOrdinary(JSContext* cx, JS::HandleObject wrapper,
+                                                  bool* isOrdinary,
+                                                  JS::MutableHandleObject protop) const
+{
+    // We want to keep the Xray's prototype distinct from that of content, but
+    // only if there's been a set.  This different-prototype-over-time behavior
+    // means that the [[GetPrototypeOf]] trap *can't* be ECMAScript's ordinary
+    // [[GetPrototypeOf]].  This also covers cross-origin Window behavior that
+    // per <https://html.spec.whatwg.org/multipage/browsers.html#windowproxy-getprototypeof>
+    // must be non-ordinary.
+    *isOrdinary = false;
+    return true;
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::setImmutablePrototype(JSContext* cx, JS::HandleObject wrapper,
+                                                 bool* succeeded) const
+{
+    // For now, lacking an obvious place to store a bit, prohibit making an
+    // Xray's [[Prototype]] immutable.  We can revisit this (or maybe give all
+    // Xrays immutable [[Prototype]], because who does this, really?) later if
+    // necessary.
+    *succeeded = false;
+    return true;
+}
+
+template <typename Base, typename Traits>
+bool
+XrayWrapper<Base, Traits>::getPropertyKeys(JSContext* cx, HandleObject wrapper, unsigned flags,
+                                           AutoIdVector& props) const
+{
+    assertEnteredPolicy(cx, wrapper, JSID_VOID, BaseProxyHandler::ENUMERATE);
+
+    // Enumerate expando properties first. Note that the expando object lives
+    // in the target compartment.
+    RootedObject target(cx, Traits::singleton.getTargetObject(wrapper));
+    RootedObject expando(cx);
+    if (!Traits::singleton.getExpandoObject(cx, target, wrapper, &expando))
+        return false;
+
+    if (expando) {
+        JSAutoCompartment ac(cx, expando);
+        if (!js::GetPropertyKeys(cx, expando, flags, &props))
+            return false;
+    }
+
+    return Traits::singleton.enumerateNames(cx, wrapper, flags, props);
+}
+
+/*
+ * The Permissive / Security variants should be used depending on whether the
+ * compartment of the wrapper is guranteed to subsume the compartment of the
+ * wrapped object (i.e. - whether it is safe from a security perspective to
+ * unwrap the wrapper).
+ */
+
+template<typename Base, typename Traits>
+const xpc::XrayWrapper<Base, Traits>
+xpc::XrayWrapper<Base, Traits>::singleton(0);
+
+template class PermissiveXrayXPCWN;
+template class SecurityXrayXPCWN;
+template class PermissiveXrayDOM;
+template class SecurityXrayDOM;
+template class PermissiveXrayJS;
+template class PermissiveXrayOpaque;
+
+} // namespace xpc