diff -r 000000000000 -r 6474c204b198 xpcom/glue/nsWeakReference.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/glue/nsWeakReference.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,130 @@
+/* -*- Mode: C++; tab-width: 2; 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/. */
+
+// nsWeakReference.cpp
+
+#include "mozilla/Attributes.h"
+
+#include "nsWeakReference.h"
+#include "nsCOMPtr.h"
+
+class nsWeakReference MOZ_FINAL : public nsIWeakReference
+  {
+    public:
+    // nsISupports...
+      NS_DECL_ISUPPORTS
+
+    // nsIWeakReference...
+      NS_DECL_NSIWEAKREFERENCE
+
+    private:
+      friend class nsSupportsWeakReference;
+
+      nsWeakReference( nsSupportsWeakReference* referent )
+          : mReferent(referent)
+          // ...I can only be constructed by an |nsSupportsWeakReference|
+        {
+          // nothing else to do here
+        }
+
+      ~nsWeakReference()
+           // ...I will only be destroyed by calling |delete| myself.
+        {
+          if ( mReferent )
+            mReferent->NoticeProxyDestruction();
+        }
+
+      void
+      NoticeReferentDestruction()
+          // ...called (only) by an |nsSupportsWeakReference| from _its_ dtor.
+        {
+          mReferent = 0;
+        }
+
+      nsSupportsWeakReference*  mReferent;
+  };
+
+nsresult
+nsQueryReferent::operator()( const nsIID& aIID, void** answer ) const
+  {
+    nsresult status;
+    if ( mWeakPtr )
+      {
+        if ( NS_FAILED(status = mWeakPtr->QueryReferent(aIID, answer)) )
+          *answer = 0;
+      }
+    else
+      status = NS_ERROR_NULL_POINTER;
+
+    if ( mErrorPtr )
+      *mErrorPtr = status;
+    return status;
+  }
+
+NS_COM_GLUE nsIWeakReference*  // or else |already_AddRefed<nsIWeakReference>|
+NS_GetWeakReference( nsISupports* aInstancePtr, nsresult* aErrorPtr )
+  {
+    nsresult status;
+
+    nsIWeakReference* result = nullptr;
+
+    if ( aInstancePtr )
+      {
+        nsCOMPtr<nsISupportsWeakReference> factoryPtr = do_QueryInterface(aInstancePtr, &status);
+        if ( factoryPtr )
+          {
+            status = factoryPtr->GetWeakReference(&result);
+          }
+        // else, |status| has already been set by |do_QueryInterface|
+      }
+    else
+      status = NS_ERROR_NULL_POINTER;
+
+    if ( aErrorPtr )
+      *aErrorPtr = status;
+    return result;
+  }
+
+NS_COM_GLUE nsresult
+nsSupportsWeakReference::GetWeakReference( nsIWeakReference** aInstancePtr )
+  {
+    if ( !aInstancePtr )
+      return NS_ERROR_NULL_POINTER;
+
+    if ( !mProxy )
+      mProxy = new nsWeakReference(this);
+    *aInstancePtr = mProxy;
+
+    nsresult status;
+    if ( !*aInstancePtr )
+      status = NS_ERROR_OUT_OF_MEMORY;
+    else
+      {
+        NS_ADDREF(*aInstancePtr);
+        status = NS_OK;
+      }
+
+    return status;
+  }
+
+NS_IMPL_ISUPPORTS(nsWeakReference, nsIWeakReference)
+
+NS_IMETHODIMP
+nsWeakReference::QueryReferent( const nsIID& aIID, void** aInstancePtr )
+  {
+    return mReferent ? mReferent->QueryInterface(aIID, aInstancePtr) : NS_ERROR_NULL_POINTER;
+  }
+
+void
+nsSupportsWeakReference::ClearWeakReferences()
+	{
+		if ( mProxy )
+			{
+				mProxy->NoticeReferentDestruction();
+				mProxy = 0;
+			}
+	}
+