diff -r 000000000000 -r 6474c204b198 layout/base/nsAutoLayoutPhase.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/base/nsAutoLayoutPhase.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,49 @@
+/* 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 nsAutoLayoutPhase_h
+#define nsAutoLayoutPhase_h
+
+#ifdef DEBUG
+
+// We can't forward declare an enum before C++11 which means we have to include
+// nsPresContext.h just because nsLayoutPhase is passed to the ctor.
+#include "nsPresContext.h"
+
+struct nsAutoLayoutPhase {
+  nsAutoLayoutPhase(nsPresContext* aPresContext, nsLayoutPhase aPhase);
+  ~nsAutoLayoutPhase();
+
+  void Enter();
+  void Exit();
+
+private:
+  nsPresContext* mPresContext;
+  nsLayoutPhase mPhase;
+  uint32_t mCount;
+};
+
+#define AUTO_LAYOUT_PHASE_ENTRY_POINT(pc_, phase_) \
+  nsAutoLayoutPhase autoLayoutPhase((pc_), (eLayoutPhase_##phase_))
+#define LAYOUT_PHASE_TEMP_EXIT() \
+  PR_BEGIN_MACRO \
+    autoLayoutPhase.Exit(); \
+  PR_END_MACRO
+#define LAYOUT_PHASE_TEMP_REENTER() \
+  PR_BEGIN_MACRO \
+    autoLayoutPhase.Enter(); \
+  PR_END_MACRO
+
+#else // DEBUG
+
+#define AUTO_LAYOUT_PHASE_ENTRY_POINT(pc_, phase_) \
+  PR_BEGIN_MACRO PR_END_MACRO
+#define LAYOUT_PHASE_TEMP_EXIT() \
+  PR_BEGIN_MACRO PR_END_MACRO
+#define LAYOUT_PHASE_TEMP_REENTER() \
+  PR_BEGIN_MACRO PR_END_MACRO
+
+#endif // DEBUG
+
+#endif // nsAutoLayoutPhase_h