Send FrameSwapMessageQueue's messages with a separate IPC

content/renderer/gpu/frame_swap_message_queue.h

Index: content/renderer/gpu/frame_swap_message_queue.h
diff --git a/content/renderer/gpu/frame_swap_message_queue.h b/content/renderer/gpu/frame_swap_message_queue.h
index 88a3731bb4b5c286c4d7296c933c1a106ccd7380..0b9e1c14a01dd50c8e3d950c837d0d3f365499bc 100644
--- a/content/renderer/gpu/frame_swap_message_queue.h
+++ b/content/renderer/gpu/frame_swap_message_queue.h
@@ -25,8 +25,10 @@ namespace content {
 
 class FrameSwapMessageSubQueue;
 
-// Queue used to keep track of which IPC::Messages should be sent along with a
-// particular compositor frame swap.
+// Queue used to keep track of which IPC::Messages should be sent after a
+// particular compositor frame swap. The messages are guaranteed to be processed
+// after the frame is processed, but there is no guarantee that nothing else
+// happens between processing the frame and processing the messages.
 class CONTENT_EXPORT FrameSwapMessageQueue
     : public base::RefCountedThreadSafe<FrameSwapMessageQueue> {
  public:
@@ -94,6 +96,8 @@ class CONTENT_EXPORT FrameSwapMessageQueue
       std::vector<std::unique_ptr<IPC::Message>>* source,
       std::vector<IPC::Message>* dest);
 
+  uint32_t AllocateFrameToken();
+
  private:
   friend class base::RefCountedThreadSafe<FrameSwapMessageQueue>;
 
@@ -105,6 +109,7 @@ class CONTENT_EXPORT FrameSwapMessageQueue
   std::unique_ptr<FrameSwapMessageSubQueue> visual_state_queue_;
   std::unique_ptr<FrameSwapMessageSubQueue> swap_queue_;
   std::vector<std::unique_ptr<IPC::Message>> next_drain_messages_;
+  uint32_t last_used_frame_token_ = 0;
 
   DISALLOW_COPY_AND_ASSIGN(FrameSwapMessageQueue);
 };