Bug 1330843 - Allow JS to create NAC pseudo-elements

Tag #1375

2 files changed, 14 insertions, 2 deletions

diff --git a/layout/style/nsCSSPseudoElements.h b/layout/style/nsCSSPseudoElements.h
index acf818a2c..64eb2f00c 100644
--- a/layout/style/nsCSSPseudoElements.h
+++ b/layout/style/nsCSSPseudoElements.h
@@ -36,6 +36,10 @@
 #define CSS_PSEUDO_ELEMENT_SUPPORTS_USER_ACTION_STATE  (1<<3)
 // Is content prevented from parsing selectors containing this pseudo-element?
 #define CSS_PSEUDO_ELEMENT_UA_SHEET_ONLY               (1<<4)
+// Can we use the ChromeOnly document.createElement(..., { pseudo: "::foo" })
+// API for creating pseudo-implementing native anonymous content in JS with this
+// pseudo-element?
+#define CSS_PSEUDO_ELEMENT_IS_JS_CREATED_NAC           (1<<5)
 
 namespace mozilla {
 
@@ -98,6 +102,11 @@ public:
 
   static bool PseudoElementSupportsUserActionState(const Type aType);
 
+  static bool PseudoElementIsJSCreatedNAC(Type aType)
+  {
+    return PseudoElementHasFlags(aType, CSS_PSEUDO_ELEMENT_IS_JS_CREATED_NAC);
+  }
+
   static bool IsEnabled(Type aType, EnabledState aEnabledState)
   {
     return !PseudoElementHasFlags(aType, CSS_PSEUDO_ELEMENT_UA_SHEET_ONLY) ||
diff --git a/layout/style/nsComputedDOMStyle.cpp b/layout/style/nsComputedDOMStyle.cpp
index 910c1de8a..102e0df18 100644
--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -717,7 +717,9 @@ nsComputedDOMStyle::UpdateCurrentStyleSources(bool aNeedsLayoutFlush)
       // We want to check that going through this path because of
       // HasPseudoElementData is rare, because it slows us down a good
       // bit.  So check that we're really inside something associated
-      // with a pseudo-element that contains elements.
+      // with a pseudo-element that contains elements.  (We also allow
+      // the element to be NAC, just in case some chrome JS calls
+      // getComputedStyle on a NAC-implemented pseudo.)
       nsStyleContext* topWithPseudoElementData = mStyleContext;
       while (topWithPseudoElementData->GetParent()->HasPseudoElementData()) {
         topWithPseudoElementData = topWithPseudoElementData->GetParent();
@@ -728,7 +730,8 @@ nsComputedDOMStyle::UpdateCurrentStyleSources(bool aNeedsLayoutFlush)
         NS_LITERAL_STRING("we should be in a pseudo-element that is expected to contain elements ("));
       assertMsg.Append(nsDependentString(pseudoAtom->GetUTF16String()));
       assertMsg.Append(')');
-      NS_ASSERTION(nsCSSPseudoElements::PseudoElementContainsElements(pseudo),
+      NS_ASSERTION(nsCSSPseudoElements::PseudoElementContainsElements(pseudo) ||
+                   mElement->IsNativeAnonymous(),
                    NS_LossyConvertUTF16toASCII(assertMsg).get());
     }
 #endif