Send FrameSwapMessageQueue's messages with a separate IPC

content/browser/renderer_host/render_widget_host_impl.h

Index: content/browser/renderer_host/render_widget_host_impl.h
diff --git a/content/browser/renderer_host/render_widget_host_impl.h b/content/browser/renderer_host/render_widget_host_impl.h
index f7015d07c3c8e12f8815abd88f9bd6ec8916d19c..c6c682fa6e90c08649c1d8bf22a845ae0c4683ce 100644
--- a/content/browser/renderer_host/render_widget_host_impl.h
+++ b/content/browser/renderer_host/render_widget_host_impl.h
@@ -667,6 +667,8 @@ class CONTENT_EXPORT RenderWidgetHostImpl : public RenderWidgetHost,
                        const gfx::Vector2d& bitmap_offset_in_dip,
                        const DragEventSourceInfo& event_info);
   void OnUpdateDragCursor(blink::WebDragOperation current_op);
+  void OnFrameSwapMessagesReceived(uint32_t frame_token,
+                                   std::vector<IPC::Message> messages);
 
   // Called (either immediately or asynchronously) after we're done with our
   // BackingStore and can send an ACK to the renderer so it can paint onto it
@@ -741,6 +743,14 @@ class CONTENT_EXPORT RenderWidgetHostImpl : public RenderWidgetHost,
   // Used for UMA logging how long the renderer was unresponsive.
   void LogHangMonitorUnresponsive();
 
+  // Signals that a frame with token |frame_token| was finished processing. If
+  // there are any queued messages belonging to it, they will be processed.
+  void DidProcessFrame(uint32_t frame_token);
+
+  // Once both the frame and its swap messages arrive, we call this method to
+  // process the messages. Virtual for tests.
+  virtual void ProcessSwapMessages(std::vector<IPC::Message> messages);
+
   // true if a renderer has once been valid. We use this flag to display a sad
   // tab only when we lose our renderer and not if a paint occurs during
   // initialization.
@@ -955,6 +965,14 @@ class CONTENT_EXPORT RenderWidgetHostImpl : public RenderWidgetHost,
 
   cc::CompositorFrameMetadata last_frame_metadata_;
 
+  // Last non-zero frame token received from the renderer. Any swap messsages
+  // having a token less than or equal to this value will be processed.
+  uint32_t last_received_frame_token_ = 0;
+
+  // List of all swap messages that their corresponding frames have not arrived.
+  // Sorted by frame token.
+  std::queue<std::pair<uint32_t, std::vector<IPC::Message>>> queued_messages_;
+
   base::WeakPtrFactory<RenderWidgetHostImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostImpl);