diff -r 000000000000 -r 6474c204b198 widget/xpwidgets/WidgetUtils.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/widget/xpwidgets/WidgetUtils.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,38 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: sw=2 ts=8 et :
+ */
+/* 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/. */
+
+#include "mozilla/WidgetUtils.h"
+
+namespace mozilla {
+
+gfx::Matrix
+ComputeTransformForRotation(const nsIntRect& aBounds,
+                              ScreenRotation aRotation)
+{
+    gfx::Matrix transform;
+    switch (aRotation) {
+    case ROTATION_0:
+        break;
+    case ROTATION_90:
+        transform.Translate(aBounds.width, 0);
+        transform = gfx::Matrix::Rotation(M_PI / 2) * transform;
+        break;
+    case ROTATION_180:
+        transform.Translate(aBounds.width, aBounds.height);
+        transform = gfx::Matrix::Rotation(M_PI) * transform;
+        break;
+    case ROTATION_270:
+        transform.Translate(0, aBounds.height);
+        transform = gfx::Matrix::Rotation(M_PI * 3 / 2) * transform;
+        break;
+    default:
+        MOZ_CRASH("Unknown rotation");
+    }
+    return transform;
+}
+
+} // namespace mozilla