diff -r 000000000000 -r 6474c204b198 layout/mathml/nsMathMLmrowFrame.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/mathml/nsMathMLmrowFrame.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,52 @@
+/* -*- 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/. */
+
+#ifndef nsMathMLmrowFrame_h___
+#define nsMathMLmrowFrame_h___
+
+#include "mozilla/Attributes.h"
+#include "nsMathMLContainerFrame.h"
+
+//
+// <mrow> -- horizontally group any number of subexpressions 
+//
+
+class nsMathMLmrowFrame : public nsMathMLContainerFrame {
+public:
+  NS_DECL_FRAMEARENA_HELPERS
+
+  friend nsIFrame* NS_NewMathMLmrowFrame(nsIPresShell* aPresShell, nsStyleContext* aContext);
+
+  virtual nsresult
+  AttributeChanged(int32_t  aNameSpaceID,
+                   nsIAtom* aAttribute,
+                   int32_t  aModType) MOZ_OVERRIDE;
+
+  NS_IMETHOD
+  InheritAutomaticData(nsIFrame* aParent) MOZ_OVERRIDE;
+
+  NS_IMETHOD
+  TransmitAutomaticData() MOZ_OVERRIDE {
+    return TransmitAutomaticDataForMrowLikeElement();
+  }
+
+  virtual eMathMLFrameType
+  GetMathMLFrameType() MOZ_OVERRIDE; 
+
+  bool
+  IsMrowLike() MOZ_OVERRIDE {
+    // <mrow> elements with a single child are treated identically to the case
+    // where the child wasn't within an mrow, so we pretend the mrow isn't an
+    // mrow in that situation.
+    return mFrames.FirstChild() != mFrames.LastChild() ||
+           !mFrames.FirstChild();
+  }
+
+protected:
+  nsMathMLmrowFrame(nsStyleContext* aContext) : nsMathMLContainerFrame(aContext) {}
+  virtual ~nsMathMLmrowFrame();
+};
+
+#endif /* nsMathMLmrowFrame_h___ */