diff -r 000000000000 -r 6474c204b198 layout/base/FramePropertyTable.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/base/FramePropertyTable.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,245 @@
+/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * 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 "FramePropertyTable.h"
+
+#include "mozilla/MemoryReporting.h"
+
+namespace mozilla {
+
+void
+FramePropertyTable::Set(nsIFrame* aFrame, const FramePropertyDescriptor* aProperty,
+                        void* aValue)
+{
+  NS_ASSERTION(aFrame, "Null frame?");
+  NS_ASSERTION(aProperty, "Null property?");
+
+  if (mLastFrame != aFrame || !mLastEntry) {
+    mLastFrame = aFrame;
+    mLastEntry = mEntries.PutEntry(aFrame);
+  }
+  Entry* entry = mLastEntry;
+
+  if (!entry->mProp.IsArray()) {
+    if (!entry->mProp.mProperty) {
+      // Empty entry, so we can just store our property in the empty slot
+      entry->mProp.mProperty = aProperty;
+      entry->mProp.mValue = aValue;
+      return;
+    }
+    if (entry->mProp.mProperty == aProperty) {
+      // Just overwrite the current value
+      entry->mProp.DestroyValueFor(aFrame);
+      entry->mProp.mValue = aValue;
+      return;
+    }
+
+    // We need to expand the single current entry to an array
+    PropertyValue current = entry->mProp;
+    entry->mProp.mProperty = nullptr;
+    static_assert(sizeof(nsTArray<PropertyValue>) <= sizeof(void *),
+                  "Property array must fit entirely within entry->mProp.mValue");
+    new (&entry->mProp.mValue) nsTArray<PropertyValue>(4);
+    entry->mProp.ToArray()->AppendElement(current);
+  }
+
+  nsTArray<PropertyValue>* array = entry->mProp.ToArray();
+  nsTArray<PropertyValue>::index_type index =
+    array->IndexOf(aProperty, 0, PropertyComparator());
+  if (index != nsTArray<PropertyValue>::NoIndex) {
+    PropertyValue* pv = &array->ElementAt(index);
+    pv->DestroyValueFor(aFrame);
+    pv->mValue = aValue;
+    return;
+  }
+
+  array->AppendElement(PropertyValue(aProperty, aValue));
+}
+
+void*
+FramePropertyTable::Get(const nsIFrame* aFrame,
+                        const FramePropertyDescriptor* aProperty,
+                        bool* aFoundResult)
+{
+  NS_ASSERTION(aFrame, "Null frame?");
+  NS_ASSERTION(aProperty, "Null property?");
+
+  if (aFoundResult) {
+    *aFoundResult = false;
+  }
+
+  if (mLastFrame != aFrame) {
+    mLastFrame = const_cast<nsIFrame*>(aFrame);
+    mLastEntry = mEntries.GetEntry(mLastFrame);
+  }
+  Entry* entry = mLastEntry;
+  if (!entry)
+    return nullptr;
+
+  if (entry->mProp.mProperty == aProperty) {
+    if (aFoundResult) {
+      *aFoundResult = true;
+    }
+    return entry->mProp.mValue;
+  }
+  if (!entry->mProp.IsArray()) {
+    // There's just one property and it's not the one we want, bail
+    return nullptr;
+  }
+
+  nsTArray<PropertyValue>* array = entry->mProp.ToArray();
+  nsTArray<PropertyValue>::index_type index =
+    array->IndexOf(aProperty, 0, PropertyComparator());
+  if (index == nsTArray<PropertyValue>::NoIndex)
+    return nullptr;
+
+  if (aFoundResult) {
+    *aFoundResult = true;
+  }
+
+  return array->ElementAt(index).mValue;
+}
+
+void*
+FramePropertyTable::Remove(nsIFrame* aFrame, const FramePropertyDescriptor* aProperty,
+                           bool* aFoundResult)
+{
+  NS_ASSERTION(aFrame, "Null frame?");
+  NS_ASSERTION(aProperty, "Null property?");
+
+  if (aFoundResult) {
+    *aFoundResult = false;
+  }
+
+  if (mLastFrame != aFrame) {
+    mLastFrame = aFrame;
+    mLastEntry = mEntries.GetEntry(aFrame);
+  }
+  Entry* entry = mLastEntry;
+  if (!entry)
+    return nullptr;
+
+  if (entry->mProp.mProperty == aProperty) {
+    // There's only one entry and it's the one we want
+    void* value = entry->mProp.mValue;
+    mEntries.RawRemoveEntry(entry);
+    mLastEntry = nullptr;
+    if (aFoundResult) {
+      *aFoundResult = true;
+    }
+    return value;
+  }
+  if (!entry->mProp.IsArray()) {
+    // There's just one property and it's not the one we want, bail
+    return nullptr;
+  }
+
+  nsTArray<PropertyValue>* array = entry->mProp.ToArray();
+  nsTArray<PropertyValue>::index_type index =
+    array->IndexOf(aProperty, 0, PropertyComparator());
+  if (index == nsTArray<PropertyValue>::NoIndex) {
+    // No such property, bail
+    return nullptr;
+  }
+
+  if (aFoundResult) {
+    *aFoundResult = true;
+  }
+
+  void* result = array->ElementAt(index).mValue;
+
+  uint32_t last = array->Length() - 1;
+  array->ElementAt(index) = array->ElementAt(last);
+  array->RemoveElementAt(last);
+
+  if (last == 1) {
+    PropertyValue pv = array->ElementAt(0);
+    array->~nsTArray<PropertyValue>();
+    entry->mProp = pv;
+  }
+  
+  return result;
+}
+
+void
+FramePropertyTable::Delete(nsIFrame* aFrame, const FramePropertyDescriptor* aProperty)
+{
+  NS_ASSERTION(aFrame, "Null frame?");
+  NS_ASSERTION(aProperty, "Null property?");
+
+  bool found;
+  void* v = Remove(aFrame, aProperty, &found);
+  if (found) {
+    PropertyValue pv(aProperty, v);
+    pv.DestroyValueFor(aFrame);
+  }
+}
+
+/* static */ void
+FramePropertyTable::DeleteAllForEntry(Entry* aEntry)
+{
+  if (!aEntry->mProp.IsArray()) {
+    aEntry->mProp.DestroyValueFor(aEntry->GetKey());
+    return;
+  }
+
+  nsTArray<PropertyValue>* array = aEntry->mProp.ToArray();
+  for (uint32_t i = 0; i < array->Length(); ++i) {
+    array->ElementAt(i).DestroyValueFor(aEntry->GetKey());
+  }
+  array->~nsTArray<PropertyValue>();
+}
+
+void
+FramePropertyTable::DeleteAllFor(nsIFrame* aFrame)
+{
+  NS_ASSERTION(aFrame, "Null frame?");
+
+  Entry* entry = mEntries.GetEntry(aFrame);
+  if (!entry)
+    return;
+
+  if (mLastFrame == aFrame) {
+    // Flush cache. We assume DeleteAllForEntry will be called before
+    // a frame is destroyed.
+    mLastFrame = nullptr;
+    mLastEntry = nullptr;
+  }
+
+  DeleteAllForEntry(entry);
+  mEntries.RawRemoveEntry(entry);
+}
+
+/* static */ PLDHashOperator
+FramePropertyTable::DeleteEnumerator(Entry* aEntry, void* aArg)
+{
+  DeleteAllForEntry(aEntry);
+  return PL_DHASH_REMOVE;
+}
+
+void
+FramePropertyTable::DeleteAll()
+{
+  mLastFrame = nullptr;
+  mLastEntry = nullptr;
+
+  mEntries.EnumerateEntries(DeleteEnumerator, nullptr);
+}
+
+size_t
+FramePropertyTable::SizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
+{
+  return mEntries.SizeOfExcludingThis(SizeOfPropertyTableEntryExcludingThis,
+                                      aMallocSizeOf);
+}
+
+/* static */ size_t
+FramePropertyTable::SizeOfPropertyTableEntryExcludingThis(Entry* aEntry,
+                      mozilla::MallocSizeOf aMallocSizeOf, void *)
+{
+  return aEntry->mProp.SizeOfExcludingThis(aMallocSizeOf);
+}
+
+}