diff -r 000000000000 -r 6474c204b198 xpcom/glue/AppData.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/glue/AppData.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,58 @@
+/* -*- Mode: C++; tab-width: 8; 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 mozilla_AppData_h
+#define mozilla_AppData_h
+
+#include "nsXREAppData.h"
+#include "nscore.h"
+#include "nsStringGlue.h"
+#include "nsISupportsUtils.h"
+
+namespace mozilla {
+
+// Like nsXREAppData, but releases all strong refs/allocated memory
+// in the destructor.
+class NS_COM_GLUE ScopedAppData : public nsXREAppData
+{
+public:
+  ScopedAppData() { Zero(); this->size = sizeof(*this); }
+
+  ScopedAppData(const nsXREAppData* aAppData);
+
+  void Zero() { memset(this, 0, sizeof(*this)); }
+
+  ~ScopedAppData();
+};
+
+/**
+ * Given "str" is holding a string allocated with NS_Alloc, or null:
+ * replace the value in "str" with a new value.
+ *
+ * @param newvalue Null is permitted. The string is cloned with
+ *                 NS_strdup
+ */
+void SetAllocatedString(const char *&str, const char *newvalue);
+
+/**
+ * Given "str" is holding a string allocated with NS_Alloc, or null:
+ * replace the value in "str" with a new value.
+ *
+ * @param newvalue If "newvalue" is the empty string, "str" will be set
+ *                 to null.
+ */
+void SetAllocatedString(const char *&str, const nsACString &newvalue);
+
+template<class T>
+void SetStrongPtr(T *&ptr, T* newvalue)
+{
+  NS_IF_RELEASE(ptr);
+  ptr = newvalue;
+  NS_IF_ADDREF(ptr);
+}
+
+} // namespace mozilla
+
+#endif