diff -r 000000000000 -r 6474c204b198 layout/base/nsStyleChangeList.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/base/nsStyleChangeList.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,129 @@
+/* -*- Mode: C++; tab-width: 2; 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/. */
+
+/*
+ * a list of the recomputation that needs to be done in response to a
+ * style change
+ */
+
+#include "nsStyleChangeList.h"
+#include "nsIContent.h"
+
+static const uint32_t kGrowArrayBy = 10;
+
+nsStyleChangeList::nsStyleChangeList()
+  : mArray(mBuffer),
+    mArraySize(kStyleChangeBufferSize),
+    mCount(0)
+{
+  MOZ_COUNT_CTOR(nsStyleChangeList);
+}
+
+nsStyleChangeList::~nsStyleChangeList()
+{
+  MOZ_COUNT_DTOR(nsStyleChangeList);
+  Clear();
+}
+
+nsresult 
+nsStyleChangeList::ChangeAt(int32_t aIndex, nsIFrame*& aFrame, nsIContent*& aContent, 
+                            nsChangeHint& aHint) const
+{
+  if ((0 <= aIndex) && (aIndex < mCount)) {
+    aFrame = mArray[aIndex].mFrame;
+    aContent = mArray[aIndex].mContent;
+    aHint = mArray[aIndex].mHint;
+    return NS_OK;
+  }
+  return NS_ERROR_ILLEGAL_VALUE;
+}
+
+nsresult 
+nsStyleChangeList::ChangeAt(int32_t aIndex, const nsStyleChangeData** aChangeData) const
+{
+  if ((0 <= aIndex) && (aIndex < mCount)) {
+    *aChangeData = &mArray[aIndex];
+    return NS_OK;
+  }
+  return NS_ERROR_ILLEGAL_VALUE;
+}
+
+nsresult 
+nsStyleChangeList::AppendChange(nsIFrame* aFrame, nsIContent* aContent, nsChangeHint aHint)
+{
+  NS_ASSERTION(aFrame || (aHint & nsChangeHint_ReconstructFrame),
+               "must have frame");
+  NS_ASSERTION(aContent || !(aHint & nsChangeHint_ReconstructFrame),
+               "must have content");
+  // XXXbz we should make this take Element instead of nsIContent
+  NS_ASSERTION(!aContent || aContent->IsElement(),
+               "Shouldn't be trying to restyle non-elements directly");
+  NS_ASSERTION(!(aHint & nsChangeHint_AllReflowHints) ||
+               (aHint & nsChangeHint_NeedReflow),
+               "Reflow hint bits set without actually asking for a reflow");
+
+  if ((0 < mCount) && (aHint & nsChangeHint_ReconstructFrame)) { // filter out all other changes for same content
+    if (aContent) {
+      for (int32_t index = mCount - 1; index >= 0; --index) {
+        if (aContent == mArray[index].mContent) { // remove this change
+          aContent->Release();
+          mCount--;
+          if (index < mCount) { // move later changes down
+            ::memmove(&mArray[index], &mArray[index + 1], 
+                      (mCount - index) * sizeof(nsStyleChangeData));
+          }
+        }
+      }
+    }
+  }
+
+  int32_t last = mCount - 1;
+  if ((0 < mCount) && aFrame && (aFrame == mArray[last].mFrame)) { // same as last frame
+    NS_UpdateHint(mArray[last].mHint, aHint);
+  }
+  else {
+    if (mCount == mArraySize) {
+      int32_t newSize = mArraySize + kGrowArrayBy;
+      nsStyleChangeData* newArray = new nsStyleChangeData[newSize];
+      if (newArray) {
+        memcpy(newArray, mArray, mCount * sizeof(nsStyleChangeData));
+        if (mArray != mBuffer) {
+          delete [] mArray;
+        }
+        mArray = newArray;
+        mArraySize = newSize;
+      }
+      else {
+        return NS_ERROR_OUT_OF_MEMORY;
+      }
+    }
+    mArray[mCount].mFrame = aFrame;
+    mArray[mCount].mContent = aContent;
+    if (aContent) {
+      aContent->AddRef();
+    }
+    mArray[mCount].mHint = aHint;
+    mCount++;
+  }
+  return NS_OK;
+}
+
+void
+nsStyleChangeList::Clear()
+{
+  for (int32_t index = mCount - 1; index >= 0; --index) {
+    nsIContent* content = mArray[index].mContent;
+    if (content) {
+      content->Release();
+    }
+  }
+  if (mArray != mBuffer) {
+    delete [] mArray;
+    mArray = mBuffer;
+    mArraySize = kStyleChangeBufferSize;
+  }
+  mCount = 0;
+}
+