diff -r 000000000000 -r 6474c204b198 layout/generic/nsHTMLReflowMetrics.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/generic/nsHTMLReflowMetrics.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,67 @@
+/* vim: set shiftwidth=2 tabstop=8 autoindent cindent expandtab: */
+/* 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/. */
+
+/* struct containing the output from nsIFrame::Reflow */
+
+#include "nsHTMLReflowMetrics.h"
+#include "nsHTMLReflowState.h"
+
+void
+nsOverflowAreas::UnionWith(const nsOverflowAreas& aOther)
+{
+  // FIXME: We should probably change scrollable overflow to use
+  // UnionRectIncludeEmpty (but leave visual overflow using UnionRect).
+  NS_FOR_FRAME_OVERFLOW_TYPES(otype) {
+    mRects[otype].UnionRect(mRects[otype], aOther.mRects[otype]);
+  }
+}
+
+void
+nsOverflowAreas::UnionAllWith(const nsRect& aRect)
+{
+  // FIXME: We should probably change scrollable overflow to use
+  // UnionRectIncludeEmpty (but leave visual overflow using UnionRect).
+  NS_FOR_FRAME_OVERFLOW_TYPES(otype) {
+    mRects[otype].UnionRect(mRects[otype], aRect);
+  }
+}
+
+void
+nsOverflowAreas::SetAllTo(const nsRect& aRect)
+{
+  NS_FOR_FRAME_OVERFLOW_TYPES(otype) {
+    mRects[otype] = aRect;
+  }
+}
+
+nsHTMLReflowMetrics::nsHTMLReflowMetrics(const nsHTMLReflowState& aState,
+                                         uint32_t aFlags)
+  : mISize(0)
+  , mBSize(0)
+  , mBlockStartAscent(ASK_FOR_BASELINE)
+  , mFlags(aFlags)
+  , mWritingMode(aState.GetWritingMode())
+{
+}
+
+void
+nsHTMLReflowMetrics::SetOverflowAreasToDesiredBounds()
+{
+  NS_FOR_FRAME_OVERFLOW_TYPES(otype) {
+    mOverflowAreas.Overflow(otype).SetRect(0, 0, Width(), Height());
+  }
+}
+
+void
+nsHTMLReflowMetrics::UnionOverflowAreasWithDesiredBounds()
+{
+  // FIXME: We should probably change scrollable overflow to use
+  // UnionRectIncludeEmpty (but leave visual overflow using UnionRect).
+  nsRect rect(0, 0, Width(), Height());
+  NS_FOR_FRAME_OVERFLOW_TYPES(otype) {
+    nsRect& o = mOverflowAreas.Overflow(otype);
+    o.UnionRect(o, rect);
+  }
+}