diff -r 000000000000 -r 6474c204b198 xpcom/glue/nsIInterfaceRequestorUtils.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/glue/nsIInterfaceRequestorUtils.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,51 @@
+/* -*- Mode: IDL; tab-width: 4; 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 __nsInterfaceRequestorUtils_h
+#define __nsInterfaceRequestorUtils_h
+
+#include "nsCOMPtr.h"
+
+// a type-safe shortcut for calling the |GetInterface()| member function
+// T must inherit from nsIInterfaceRequestor, but the cast may be ambiguous.
+template <class T, class DestinationType>
+inline
+nsresult
+CallGetInterface( T* aSource, DestinationType** aDestination )
+  {
+    NS_PRECONDITION(aSource, "null parameter");
+    NS_PRECONDITION(aDestination, "null parameter");
+
+    return aSource->GetInterface(NS_GET_TEMPLATE_IID(DestinationType),
+                                 reinterpret_cast<void**>(aDestination));
+  }
+
+class NS_COM_GLUE nsGetInterface : public nsCOMPtr_helper
+  {
+    public:
+      nsGetInterface( nsISupports* aSource, nsresult* error )
+          : mSource(aSource),
+            mErrorPtr(error)
+        {
+          // nothing else to do here
+        }
+
+      virtual nsresult NS_FASTCALL operator()( const nsIID&, void** ) const;
+
+    private:
+      nsISupports*          mSource;
+      nsresult*             mErrorPtr;
+  };
+
+inline
+const nsGetInterface
+do_GetInterface( nsISupports* aSource, nsresult* error = 0 )
+  {
+    return nsGetInterface(aSource, error);
+  }
+
+#endif // __nsInterfaceRequestorUtils_h
+