3D Compositing in <browser>, first draft.

ipc/ipc_forwarding_message_filter.h

Index: ipc/ipc_forwarding_message_filter.h
diff --git a/ipc/ipc_forwarding_message_filter.h b/ipc/ipc_forwarding_message_filter.h
index 919a44d75994588f222f6136077a4f14ac7a972b..fe850522b09883788d7272934becd5ef9dd5f6fa 100644
--- a/ipc/ipc_forwarding_message_filter.h
+++ b/ipc/ipc_forwarding_message_filter.h
@@ -30,6 +30,8 @@ class IPC_EXPORT ForwardingMessageFilter : public ChannelProxy::MessageFilter {
   // |target_task_runner| with messages that were intercepted by this filter.
   typedef base::Callback<void(const Message&)> Handler;
 
+  typedef base::Callback<int(const Message&)> IDCallback;
+
   // This filter will intercept |message_ids_to_filter| and post
   // them to the provided |target_task_runner|, where they will be given
   // to |handler|.
@@ -40,13 +42,23 @@ class IPC_EXPORT ForwardingMessageFilter : public ChannelProxy::MessageFilter {
       size_t num_message_ids_to_filter,
       base::TaskRunner* target_task_runner);
 
-  // Define the message routes to be filtered.
+  // Define the message IDs to be filtered. By default, the ID is the message's
+  // routing ID but this can be changed with SetIDCallback.
   void AddRoute(int routing_id, const Handler& handler);
   void RemoveRoute(int routing_id);
 
+  // Set the function used to extract an ID from a message.
+  void SetIDCallback(const IDCallback& function);
+
   // ChannelProxy::MessageFilter methods:
   virtual bool OnMessageReceived(const Message& message) OVERRIDE;
 
+  // Extract the routing ID. Can be used to reset the ID function to the
+  // default.
+  static int GetMessageRoutingID(const Message& message) {
+    return message.routing_id();
+  }
+
  private:
   friend class ChannelProxy::MessageFilter;
   virtual ~ForwardingMessageFilter();
@@ -63,6 +75,9 @@ class IPC_EXPORT ForwardingMessageFilter : public ChannelProxy::MessageFilter {
   // Indicates the routing_ids for which messages should be filtered.
   std::map<int, Handler> handlers_;
 
+  // The function used for extracting IDs.
+  IDCallback id_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(ForwardingMessageFilter);
 };