diff -r 000000000000 -r 6474c204b198 xpcom/glue/AutoRestore.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/glue/AutoRestore.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,46 @@
+/* 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/. */
+
+/* functions for restoring saved values at the end of a C++ scope */
+
+#ifndef mozilla_AutoRestore_h_
+#define mozilla_AutoRestore_h_
+
+#include "mozilla/Attributes.h" // MOZ_STACK_CLASS
+#include "mozilla/GuardObjects.h"
+
+namespace mozilla {
+
+  /**
+   * Save the current value of a variable and restore it when the object
+   * goes out of scope.  For example:
+   *   {
+   *     AutoRestore<bool> savePainting(mIsPainting);
+   *     mIsPainting = true;
+   *     
+   *     // ... your code here ...
+   *
+   *     // mIsPainting is reset to its old value at the end of this block
+   *   }
+   */
+  template <class T>
+  class MOZ_STACK_CLASS AutoRestore
+  {
+  private:
+    T& mLocation;
+    T mValue;
+    MOZ_DECL_USE_GUARD_OBJECT_NOTIFIER
+  public:
+    AutoRestore(T& aValue MOZ_GUARD_OBJECT_NOTIFIER_PARAM)
+      : mLocation(aValue), mValue(aValue)
+    {
+      MOZ_GUARD_OBJECT_NOTIFIER_INIT;
+    }
+    ~AutoRestore() { mLocation = mValue; }
+  };
+
+} // namespace mozilla
+
+#endif /* !defined(mozilla_AutoRestore_h_) */