diff -r 000000000000 -r 6474c204b198 xpcom/base/nsInterfaceRequestorAgg.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/base/nsInterfaceRequestorAgg.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,87 @@
+/* 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 "nsInterfaceRequestorAgg.h"
+#include "nsIInterfaceRequestor.h"
+#include "nsCOMPtr.h"
+#include "mozilla/Attributes.h"
+#include "nsThreadUtils.h"
+#include "nsProxyRelease.h"
+
+class nsInterfaceRequestorAgg MOZ_FINAL : public nsIInterfaceRequestor
+{
+public:
+  // XXX This needs to support threadsafe refcounting until we fix bug 243591.
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIINTERFACEREQUESTOR
+
+  nsInterfaceRequestorAgg(nsIInterfaceRequestor *aFirst,
+                          nsIInterfaceRequestor *aSecond,
+                          nsIEventTarget *aConsumerTarget = nullptr)
+    : mFirst(aFirst)
+    , mSecond(aSecond)
+    , mConsumerTarget(aConsumerTarget)
+  {
+    if (!mConsumerTarget) {
+      mConsumerTarget = NS_GetCurrentThread();
+    }
+  }
+  ~nsInterfaceRequestorAgg();
+
+private:
+  nsCOMPtr<nsIInterfaceRequestor> mFirst, mSecond;
+  nsCOMPtr<nsIEventTarget> mConsumerTarget;
+};
+
+NS_IMPL_ISUPPORTS(nsInterfaceRequestorAgg, nsIInterfaceRequestor)
+
+NS_IMETHODIMP
+nsInterfaceRequestorAgg::GetInterface(const nsIID &aIID, void **aResult)
+{
+  nsresult rv = NS_ERROR_NO_INTERFACE;
+  if (mFirst)
+    rv = mFirst->GetInterface(aIID, aResult);
+  if (mSecond && NS_FAILED(rv))
+    rv = mSecond->GetInterface(aIID, aResult);
+  return rv;
+}
+
+nsInterfaceRequestorAgg::~nsInterfaceRequestorAgg()
+{
+  nsIInterfaceRequestor* iir = nullptr;
+  mFirst.swap(iir);
+  if (iir) {
+    NS_ProxyRelease(mConsumerTarget, iir);
+  }
+  iir = nullptr;
+  mSecond.swap(iir);
+  if (iir) {
+    NS_ProxyRelease(mConsumerTarget, iir);
+  }
+}
+
+nsresult
+NS_NewInterfaceRequestorAggregation(nsIInterfaceRequestor *aFirst,
+                                    nsIInterfaceRequestor *aSecond,
+                                    nsIInterfaceRequestor **aResult)
+{
+  *aResult = new nsInterfaceRequestorAgg(aFirst, aSecond);
+  if (!*aResult)
+    return NS_ERROR_OUT_OF_MEMORY;
+  NS_ADDREF(*aResult);
+  return NS_OK;
+}
+
+nsresult
+NS_NewInterfaceRequestorAggregation(nsIInterfaceRequestor *aFirst,
+                                    nsIInterfaceRequestor *aSecond,
+                                    nsIEventTarget* aTarget,
+                                    nsIInterfaceRequestor **aResult)
+{
+  *aResult = new nsInterfaceRequestorAgg(aFirst, aSecond, aTarget);
+  if (!*aResult)
+    return NS_ERROR_OUT_OF_MEMORY;
+  NS_ADDREF(*aResult);
+  return NS_OK;
+}