diff -r 000000000000 -r 6474c204b198 layout/xul/grid/nsGridRowGroupFrame.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/xul/grid/nsGridRowGroupFrame.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,63 @@
+/* -*- 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/. */
+
+//
+// Eric Vaughan
+// Netscape Communications
+//
+// See documentation in associated header file
+//
+
+#include "nsGridRowGroupFrame.h"
+#include "nsGridRowLeafLayout.h"
+#include "nsGridRow.h"
+#include "nsBoxLayoutState.h"
+#include "nsGridLayout2.h"
+
+already_AddRefed<nsBoxLayout> NS_NewGridRowGroupLayout();
+
+nsIFrame*
+NS_NewGridRowGroupFrame(nsIPresShell* aPresShell,
+                        nsStyleContext* aContext)
+{
+  nsCOMPtr<nsBoxLayout> layout = NS_NewGridRowGroupLayout();
+  return new (aPresShell) nsGridRowGroupFrame(aPresShell, aContext, layout);
+}
+
+NS_IMPL_FRAMEARENA_HELPERS(nsGridRowGroupFrame)
+
+
+/**
+ * This is redefined because row groups have a funny property. If they are flexible
+ * then their flex must be equal to the sum of their children's flexes.
+ */
+nscoord
+nsGridRowGroupFrame::GetFlex(nsBoxLayoutState& aState)
+{
+  // if we are flexible out flexibility is determined by our columns.
+  // so first get the our flex. If not 0 then our flex is the sum of
+  // our columns flexes.
+
+  if (!DoesNeedRecalc(mFlex))
+     return mFlex;
+
+  if (nsBoxFrame::GetFlex(aState) == 0)
+    return 0;
+
+  // ok we are flexible add up our children
+  nscoord totalFlex = 0;
+  nsIFrame* child = GetChildBox();
+  while (child)
+  {
+    totalFlex += child->GetFlex(aState);
+    child = child->GetNextBox();
+  }
+
+  mFlex = totalFlex;
+
+  return totalFlex;
+}
+
+