Add m-esr52 at 52.6.0

1 files changed, 607 insertions, 0 deletions

diff --git a/dom/svg/DOMSVGPathSegList.cpp b/dom/svg/DOMSVGPathSegList.cpp
new file mode 100644
index 000000000..edacdfc93
--- /dev/null
+++ b/dom/svg/DOMSVGPathSegList.cpp
@@ -0,0 +1,607 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 "nsSVGElement.h"
+#include "DOMSVGPathSegList.h"
+#include "DOMSVGPathSeg.h"
+#include "nsError.h"
+#include "SVGAnimatedPathSegList.h"
+#include "nsCOMPtr.h"
+#include "nsSVGAttrTearoffTable.h"
+#include "SVGPathSegUtils.h"
+#include "mozilla/dom/SVGPathSegListBinding.h"
+
+// See the comment in this file's header.
+
+namespace mozilla {
+
+  static inline
+nsSVGAttrTearoffTable<void, DOMSVGPathSegList>&
+SVGPathSegListTearoffTable()
+{
+  static nsSVGAttrTearoffTable<void, DOMSVGPathSegList>
+    sSVGPathSegListTearoffTable;
+  return sSVGPathSegListTearoffTable;
+}
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(DOMSVGPathSegList)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(DOMSVGPathSegList)
+  // No unlinking of mElement, we'd need to null out the value pointer (the
+  // object it points to is held by the element) and null-check it everywhere.
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(DOMSVGPathSegList)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mElement)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(DOMSVGPathSegList)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(DOMSVGPathSegList)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(DOMSVGPathSegList)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(DOMSVGPathSegList)
+  NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+
+//----------------------------------------------------------------------
+// Helper class: AutoChangePathSegListNotifier
+// Stack-based helper class to pair calls to WillChangePathSegList and
+// DidChangePathSegList.
+class MOZ_RAII AutoChangePathSegListNotifier
+{
+public:
+  explicit AutoChangePathSegListNotifier(DOMSVGPathSegList* aPathSegList MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+    : mPathSegList(aPathSegList)
+  {
+    MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+    MOZ_ASSERT(mPathSegList, "Expecting non-null pathSegList");
+    mEmptyOrOldValue =
+      mPathSegList->Element()->WillChangePathSegList();
+  }
+
+  ~AutoChangePathSegListNotifier()
+  {
+    mPathSegList->Element()->DidChangePathSegList(mEmptyOrOldValue);
+    if (mPathSegList->AttrIsAnimating()) {
+      mPathSegList->Element()->AnimationNeedsResample();
+    }
+  }
+
+private:
+  DOMSVGPathSegList* const mPathSegList;
+  nsAttrValue        mEmptyOrOldValue;
+  MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
+};
+
+/* static */ already_AddRefed<DOMSVGPathSegList>
+DOMSVGPathSegList::GetDOMWrapper(void *aList,
+                                 nsSVGElement *aElement,
+                                 bool aIsAnimValList)
+{
+  RefPtr<DOMSVGPathSegList> wrapper =
+    SVGPathSegListTearoffTable().GetTearoff(aList);
+  if (!wrapper) {
+    wrapper = new DOMSVGPathSegList(aElement, aIsAnimValList);
+    SVGPathSegListTearoffTable().AddTearoff(aList, wrapper);
+  }
+  return wrapper.forget();
+}
+
+/* static */ DOMSVGPathSegList*
+DOMSVGPathSegList::GetDOMWrapperIfExists(void *aList)
+{
+  return SVGPathSegListTearoffTable().GetTearoff(aList);
+}
+
+DOMSVGPathSegList::~DOMSVGPathSegList()
+{
+  // There are now no longer any references to us held by script or list items.
+  // Note we must use GetAnimValKey/GetBaseValKey here, NOT InternalList()!
+  void *key = mIsAnimValList ?
+    InternalAList().GetAnimValKey() :
+    InternalAList().GetBaseValKey();
+  SVGPathSegListTearoffTable().RemoveTearoff(key);
+}
+
+JSObject*
+DOMSVGPathSegList::WrapObject(JSContext *cx, JS::Handle<JSObject*> aGivenProto)
+{
+  return mozilla::dom::SVGPathSegListBinding::Wrap(cx, this, aGivenProto);
+}
+
+void
+DOMSVGPathSegList::InternalListWillChangeTo(const SVGPathData& aNewValue)
+{
+  // When the number of items in our internal counterpart changes, we MUST stay
+  // in sync. Everything in the scary comment in
+  // DOMSVGLengthList::InternalBaseValListWillChangeTo applies here just as
+  // much, but we have the additional issue that failing to stay in sync would
+  // mean that - assuming we aren't reading bad memory - we would likely end up
+  // decoding command types from argument floats when looking in our
+  // SVGPathData's data array! Either way, we'll likely then go down
+  // NS_NOTREACHED code paths, or end up reading/setting more bad memory!!
+
+  // The only time that our other DOM list type implementations remove items is
+  // if those items become surplus items due to an attribute change or SMIL
+  // animation sample shortening the list. In general though, they try to keep
+  // their existing DOM items, even when things change. To be consistent, we'd
+  // really like to do the same thing. However, because different types of path
+  // segment correspond to different DOMSVGPathSeg subclasses, the type of
+  // items in our list are generally not the same, which makes this harder for
+  // us. We have to remove DOM segments if their type is not the same as the
+  // type of the new internal segment at their index.
+  //
+  // We also need to sync up mInternalDataIndex, but since we need to loop over
+  // all the items in the new list checking types anyway, that's almost
+  // insignificant in terms of overhead.
+  //
+  // Note that this method is called on every single SMIL animation resample
+  // and we have no way to short circuit the overhead since we don't have a
+  // way to tell if the call is due to a new animation, or a resample of an
+  // existing animation (when the number and type of items would be the same).
+  // (Note that a new animation could start overriding an existing animation at
+  // any time, so checking IsAnimating() wouldn't work.) Because we get called
+  // on every sample, it would not be acceptable alternative to throw away all
+  // our items and let them be recreated lazily, since that would break what
+  // script sees!
+
+  uint32_t length = mItems.Length();
+  uint32_t index = 0;
+
+  uint32_t dataLength = aNewValue.mData.Length();
+  uint32_t dataIndex = 0; // index into aNewValue's raw data array
+
+  uint32_t newSegType;
+
+  RefPtr<DOMSVGPathSegList> kungFuDeathGrip;
+  if (length) {
+    // RemovingFromList() might clear last reference to |this|.
+    // Retain a temporary reference to keep from dying before returning.
+    //
+    // NOTE: For path-seg lists (unlike other list types), we have to do this
+    // *whenever our list is nonempty* (even if we're growing in length).
+    // That's because the path-seg-type of any segment could differ between old
+    // list vs. new list, which will make us destroy & recreate that segment,
+    // which could remove the last reference to us.
+    //
+    // (We explicitly *don't* want to create a kungFuDeathGrip in the length=0
+    // case, though, because we do hit this code inside our constructor before
+    // any other owning references have been added, and at that point, the
+    // deathgrip-removal would make us die before we exit our constructor.)
+    kungFuDeathGrip = this;
+  }
+
+  while (index < length && dataIndex < dataLength) {
+    newSegType = SVGPathSegUtils::DecodeType(aNewValue.mData[dataIndex]);
+    if (ItemAt(index) && ItemAt(index)->Type() != newSegType) {
+      ItemAt(index)->RemovingFromList();
+      ItemAt(index) = nullptr;
+    }
+    // Only after the RemovingFromList() can we touch mInternalDataIndex!
+    mItems[index].mInternalDataIndex = dataIndex;
+    ++index;
+    dataIndex += 1 + SVGPathSegUtils::ArgCountForType(newSegType);
+  }
+
+  MOZ_ASSERT((index == length && dataIndex <= dataLength) ||
+             (index <= length && dataIndex == dataLength),
+             "very bad - list corruption?");
+
+  if (index < length) {
+    // aNewValue has fewer items than our previous internal counterpart
+
+    uint32_t newLength = index;
+
+    // Remove excess items from the list:
+    for (; index < length; ++index) {
+      if (ItemAt(index)) {
+        ItemAt(index)->RemovingFromList();
+        ItemAt(index) = nullptr;
+      }
+    }
+
+    // Only now may we truncate mItems
+    mItems.TruncateLength(newLength);
+  } else if (dataIndex < dataLength) {
+    // aNewValue has more items than our previous internal counterpart
+
+    // Sync mItems:
+    while (dataIndex < dataLength) {
+      if (mItems.Length() &&
+          mItems.Length() - 1 > DOMSVGPathSeg::MaxListIndex()) {
+        // It's safe to get out of sync with our internal list as long as we
+        // have FEWER items than it does.
+        return;
+      }
+      if (!mItems.AppendElement(ItemProxy(nullptr, dataIndex), fallible)) {
+        // OOM
+        ErrorResult rv;
+        Clear(rv);
+        MOZ_ASSERT(!rv.Failed());
+        return;
+      }
+      dataIndex += 1 + SVGPathSegUtils::ArgCountForType(SVGPathSegUtils::DecodeType(aNewValue.mData[dataIndex]));
+    }
+  }
+
+  MOZ_ASSERT(dataIndex == dataLength, "Serious processing error");
+  MOZ_ASSERT(index == length, "Serious counting error");
+}
+
+bool
+DOMSVGPathSegList::AttrIsAnimating() const
+{
+  return InternalAList().IsAnimating();
+}
+
+bool
+DOMSVGPathSegList::AnimListMirrorsBaseList() const
+{
+  return GetDOMWrapperIfExists(InternalAList().GetAnimValKey()) &&
+           !AttrIsAnimating();
+}
+ 
+SVGPathData&
+DOMSVGPathSegList::InternalList() const
+{
+  SVGAnimatedPathSegList *alist = mElement->GetAnimPathSegList();
+  return mIsAnimValList && alist->IsAnimating() ? *alist->mAnimVal : alist->mBaseVal;
+}
+
+SVGAnimatedPathSegList&
+DOMSVGPathSegList::InternalAList() const
+{
+  MOZ_ASSERT(mElement->GetAnimPathSegList(), "Internal error");
+  return *mElement->GetAnimPathSegList();
+}
+
+// ----------------------------------------------------------------------------
+// nsIDOMSVGPathSegList implementation:
+
+void
+DOMSVGPathSegList::Clear(ErrorResult& aError)
+{
+  if (IsAnimValList()) {
+    aError.Throw(NS_ERROR_DOM_NO_MODIFICATION_ALLOWED_ERR);
+    return;
+  }
+
+  if (LengthNoFlush() > 0) {
+    AutoChangePathSegListNotifier notifier(this);
+    // DOM list items that are to be removed must be removed before we change
+    // the internal list, otherwise they wouldn't be able to copy their
+    // internal counterparts' values!
+
+    InternalListWillChangeTo(SVGPathData()); // clears mItems
+
+    if (!AttrIsAnimating()) {
+      // The anim val list is in sync with the base val list
+      DOMSVGPathSegList *animList =
+        GetDOMWrapperIfExists(InternalAList().GetAnimValKey());
+      if (animList) {
+        animList->InternalListWillChangeTo(SVGPathData()); // clears its mItems
+      }
+    }
+
+    InternalList().Clear();
+  }
+}
+
+already_AddRefed<DOMSVGPathSeg>
+DOMSVGPathSegList::Initialize(DOMSVGPathSeg& aNewItem, ErrorResult& aError)
+{
+  if (IsAnimValList()) {
+    aError.Throw(NS_ERROR_DOM_NO_MODIFICATION_ALLOWED_ERR);
+    return nullptr;
+  }
+
+  // If aNewItem is already in a list we should insert a clone of aNewItem,
+  // and for consistency, this should happen even if *this* is the list that
+  // aNewItem is currently in. Note that in the case of aNewItem being in this
+  // list, the Clear() call before the InsertItemBefore() call would remove it
+  // from this list, and so the InsertItemBefore() call would not insert a
+  // clone of aNewItem, it would actually insert aNewItem. To prevent that
+  // from happening we have to do the clone here, if necessary.
+
+  RefPtr<DOMSVGPathSeg> domItem = &aNewItem;
+  if (aNewItem.HasOwner()) {
+    domItem = aNewItem.Clone();
+  }
+
+  Clear(aError);
+  MOZ_ASSERT(!aError.Failed(), "How could this fail?");
+  return InsertItemBefore(*domItem, 0, aError);
+}
+
+already_AddRefed<DOMSVGPathSeg>
+DOMSVGPathSegList::GetItem(uint32_t index, ErrorResult& error)
+{
+  bool found;
+  RefPtr<DOMSVGPathSeg> item = IndexedGetter(index, found, error);
+  if (!found) {
+    error.Throw(NS_ERROR_DOM_INDEX_SIZE_ERR);
+  }
+  return item.forget();
+}
+
+already_AddRefed<DOMSVGPathSeg>
+DOMSVGPathSegList::IndexedGetter(uint32_t aIndex, bool& aFound,
+                                 ErrorResult& aError)
+{
+  if (IsAnimValList()) {
+    Element()->FlushAnimations();
+  }
+  aFound = aIndex < LengthNoFlush();
+  if (aFound) {
+    return GetItemAt(aIndex);
+  }
+  return nullptr;
+}
+
+already_AddRefed<DOMSVGPathSeg>
+DOMSVGPathSegList::InsertItemBefore(DOMSVGPathSeg& aNewItem,
+                                    uint32_t aIndex,
+                                    ErrorResult& aError)
+{
+  if (IsAnimValList()) {
+    aError.Throw(NS_ERROR_DOM_NO_MODIFICATION_ALLOWED_ERR);
+    return nullptr;
+  }
+
+  uint32_t internalIndex;
+  if (aIndex < LengthNoFlush()) {
+    internalIndex = mItems[aIndex].mInternalDataIndex;
+  } else {
+    aIndex = LengthNoFlush();
+    internalIndex = InternalList().mData.Length();
+  }
+  if (aIndex >= DOMSVGPathSeg::MaxListIndex()) {
+    aError.Throw(NS_ERROR_DOM_INDEX_SIZE_ERR);
+    return nullptr;
+  }
+
+  RefPtr<DOMSVGPathSeg> domItem = &aNewItem;
+  if (domItem->HasOwner()) {
+    domItem = domItem->Clone(); // must do this before changing anything!
+  }
+
+  uint32_t argCount = SVGPathSegUtils::ArgCountForType(domItem->Type());
+
+  // Ensure we have enough memory so we can avoid complex error handling below:
+  if (!mItems.SetCapacity(mItems.Length() + 1, fallible) ||
+      !InternalList().mData.SetCapacity(InternalList().mData.Length() + 1 + argCount,
+                                        fallible)) {
+    aError.Throw(NS_ERROR_OUT_OF_MEMORY);
+    return nullptr;
+  }
+  if (AnimListMirrorsBaseList()) {
+    DOMSVGPathSegList *animVal =
+      GetDOMWrapperIfExists(InternalAList().GetAnimValKey());
+    MOZ_ASSERT(animVal, "animVal should be a valid pointer");
+    if (!animVal->mItems.SetCapacity(
+          animVal->mItems.Length() + 1, fallible)) {
+      aError.Throw(NS_ERROR_OUT_OF_MEMORY);
+      return nullptr;
+    }
+  }
+
+  AutoChangePathSegListNotifier notifier(this);
+  // Now that we know we're inserting, keep animVal list in sync as necessary.
+  MaybeInsertNullInAnimValListAt(aIndex, internalIndex, argCount);
+
+  float segAsRaw[1 + NS_SVG_PATH_SEG_MAX_ARGS];
+  domItem->ToSVGPathSegEncodedData(segAsRaw);
+
+  MOZ_ALWAYS_TRUE(InternalList().mData.InsertElementsAt(internalIndex,
+                                                        segAsRaw,
+                                                        1 + argCount,
+                                                        fallible));
+  MOZ_ALWAYS_TRUE(mItems.InsertElementAt(aIndex,
+                                         ItemProxy(domItem.get(),
+                                                   internalIndex),
+                                         fallible));
+
+  // This MUST come after the insertion into InternalList(), or else under the
+  // insertion into InternalList() the values read from domItem would be bad
+  // data from InternalList() itself!:
+  domItem->InsertingIntoList(this, aIndex, IsAnimValList());
+
+  UpdateListIndicesFromIndex(aIndex + 1, argCount + 1);
+
+  return domItem.forget();
+}
+
+already_AddRefed<DOMSVGPathSeg>
+DOMSVGPathSegList::ReplaceItem(DOMSVGPathSeg& aNewItem,
+                               uint32_t aIndex,
+                               ErrorResult& aError)
+{
+  if (IsAnimValList()) {
+    aError.Throw(NS_ERROR_DOM_NO_MODIFICATION_ALLOWED_ERR);
+    return nullptr;
+  }
+
+  if (aIndex >= LengthNoFlush()) {
+    aError.Throw(NS_ERROR_DOM_INDEX_SIZE_ERR);
+    return nullptr;
+  }
+
+  RefPtr<DOMSVGPathSeg> domItem = &aNewItem;
+  if (domItem->HasOwner()) {
+    domItem = domItem->Clone(); // must do this before changing anything!
+  }
+
+  AutoChangePathSegListNotifier notifier(this);
+  if (ItemAt(aIndex)) {
+    // Notify any existing DOM item of removal *before* modifying the lists so
+    // that the DOM item can copy the *old* value at its index:
+    ItemAt(aIndex)->RemovingFromList();
+  }
+
+  uint32_t internalIndex = mItems[aIndex].mInternalDataIndex;
+  // We use InternalList() to get oldArgCount since we may not have a DOM
+  // wrapper at the index being replaced.
+  uint32_t oldType = SVGPathSegUtils::DecodeType(InternalList().mData[internalIndex]);
+
+  // NOTE: ArgCountForType returns a (small) unsigned value, but we're
+  // intentionally putting it in a signed variable, because we're going to
+  // subtract these values and might produce something negative.
+  int32_t oldArgCount = SVGPathSegUtils::ArgCountForType(oldType);
+  int32_t newArgCount = SVGPathSegUtils::ArgCountForType(domItem->Type());
+
+  float segAsRaw[1 + NS_SVG_PATH_SEG_MAX_ARGS];
+  domItem->ToSVGPathSegEncodedData(segAsRaw);
+
+  if (!InternalList().mData.ReplaceElementsAt(internalIndex, 1 + oldArgCount,
+                                              segAsRaw, 1 + newArgCount,
+                                              fallible)) {
+    aError.Throw(NS_ERROR_OUT_OF_MEMORY);
+    return nullptr;
+  }
+  ItemAt(aIndex) = domItem;
+
+  // This MUST come after the ToSVGPathSegEncodedData call, otherwise that call
+  // would end up reading bad data from InternalList()!
+  domItem->InsertingIntoList(this, aIndex, IsAnimValList());
+
+  int32_t delta = newArgCount - oldArgCount;
+  if (delta != 0) {
+    for (uint32_t i = aIndex + 1; i < LengthNoFlush(); ++i) {
+      mItems[i].mInternalDataIndex += delta;
+    }
+  }
+
+  return domItem.forget();
+}
+
+already_AddRefed<DOMSVGPathSeg>
+DOMSVGPathSegList::RemoveItem(uint32_t aIndex,
+                              ErrorResult& aError)
+{
+  if (IsAnimValList()) {
+    aError.Throw(NS_ERROR_DOM_NO_MODIFICATION_ALLOWED_ERR);
+    return nullptr;
+  }
+
+  if (aIndex >= LengthNoFlush()) {
+    aError.Throw(NS_ERROR_DOM_INDEX_SIZE_ERR);
+    return nullptr;
+  }
+  // We have to return the removed item, so get it, creating it if necessary:
+  RefPtr<DOMSVGPathSeg> result = GetItemAt(aIndex);
+
+  AutoChangePathSegListNotifier notifier(this);
+  // Notify the DOM item of removal *before* modifying the lists so that the
+  // DOM item can copy its *old* value:
+  ItemAt(aIndex)->RemovingFromList();
+
+  uint32_t internalIndex = mItems[aIndex].mInternalDataIndex;
+  uint32_t segType = SVGPathSegUtils::DecodeType(InternalList().mData[internalIndex]);
+  // NOTE: ArgCountForType returns a (small) unsigned value, but we're
+  // intentionally putting it in a signed value, because we're going to
+  // negate it, and you can't negate an unsigned value.
+  int32_t argCount = SVGPathSegUtils::ArgCountForType(segType);
+
+  // Now that we know we're removing, keep animVal list in sync as necessary.
+  // Do this *before* touching InternalList() so the removed item can get its
+  // internal value.
+  MaybeRemoveItemFromAnimValListAt(aIndex, argCount);
+
+  InternalList().mData.RemoveElementsAt(internalIndex, 1 + argCount);
+  mItems.RemoveElementAt(aIndex);
+
+  UpdateListIndicesFromIndex(aIndex, -(argCount + 1));
+
+  return result.forget();
+}
+
+already_AddRefed<DOMSVGPathSeg>
+DOMSVGPathSegList::GetItemAt(uint32_t aIndex)
+{
+  MOZ_ASSERT(aIndex < mItems.Length());
+
+  if (!ItemAt(aIndex)) {
+    ItemAt(aIndex) = DOMSVGPathSeg::CreateFor(this, aIndex, IsAnimValList());
+  }
+  RefPtr<DOMSVGPathSeg> result = ItemAt(aIndex);
+  return result.forget();
+}
+
+void
+DOMSVGPathSegList::
+  MaybeInsertNullInAnimValListAt(uint32_t aIndex,
+                                 uint32_t aInternalIndex,
+                                 uint32_t aArgCountForItem)
+{
+  MOZ_ASSERT(!IsAnimValList(), "call from baseVal to animVal");
+
+  if (!AnimListMirrorsBaseList()) {
+    return;
+  }
+
+  // The anim val list is in sync with the base val list
+  DOMSVGPathSegList *animVal =
+    GetDOMWrapperIfExists(InternalAList().GetAnimValKey());
+
+  MOZ_ASSERT(animVal, "AnimListMirrorsBaseList() promised a non-null animVal");
+  MOZ_ASSERT(animVal->mItems.Length() == mItems.Length(),
+             "animVal list not in sync!");
+  MOZ_ALWAYS_TRUE(animVal->mItems.InsertElementAt(aIndex,
+                                                  ItemProxy(nullptr,
+                                                            aInternalIndex),
+                                                  fallible));
+
+  animVal->UpdateListIndicesFromIndex(aIndex + 1, 1 + aArgCountForItem);
+}
+
+void
+DOMSVGPathSegList::
+  MaybeRemoveItemFromAnimValListAt(uint32_t aIndex,
+                                   int32_t aArgCountForItem)
+{
+  MOZ_ASSERT(!IsAnimValList(), "call from baseVal to animVal");
+
+  if (!AnimListMirrorsBaseList()) {
+    return;
+  }
+
+  // This needs to be a strong reference; otherwise, the RemovingFromList call
+  // below might drop the last reference to animVal before we're done with it.
+  RefPtr<DOMSVGPathSegList> animVal =
+    GetDOMWrapperIfExists(InternalAList().GetAnimValKey());
+
+  MOZ_ASSERT(animVal, "AnimListMirrorsBaseList() promised a non-null animVal");
+  MOZ_ASSERT(animVal->mItems.Length() == mItems.Length(),
+             "animVal list not in sync!");
+
+  if (animVal->ItemAt(aIndex)) {
+    animVal->ItemAt(aIndex)->RemovingFromList();
+  }
+  animVal->mItems.RemoveElementAt(aIndex);
+
+  animVal->UpdateListIndicesFromIndex(aIndex, -(1 + aArgCountForItem));
+}
+
+void
+DOMSVGPathSegList::UpdateListIndicesFromIndex(uint32_t aStartingIndex,
+                                              int32_t  aInternalDataIndexDelta)
+{
+  uint32_t length = mItems.Length();
+
+  for (uint32_t i = aStartingIndex; i < length; ++i) {
+    mItems[i].mInternalDataIndex += aInternalDataIndexDelta;
+    if (ItemAt(i)) {
+      ItemAt(i)->UpdateListIndex(i);
+    }
+  }
+}
+
+} // namespace mozilla