Adds routed interface support between RenderFrameHost and RenderFrame

ipc/message_router.h

Index: ipc/message_router.h
diff --git a/ipc/message_router.h b/ipc/message_router.h
index db4bc271fc900e9758313e725322841149634dc3..f232896855dc4cbb34032c201bfea224a575621b 100644
--- a/ipc/message_router.h
+++ b/ipc/message_router.h
@@ -59,6 +59,9 @@ class IPC_EXPORT MessageRouter : public Listener, public Sender {
   // Called to remove a listener for a particular message routing ID.
   void RemoveRoute(int32_t routing_id);
 
+  // Returns the Listener associated with |routing_id|.
+  Listener* GetRoute(int32_t routing_id);
+
  private:
   // A list of all listeners with assigned routing IDs.
   IDMap<Listener> routes_;