Send FrameSwapMessageQueue's messages with a separate IPC

content/renderer/gpu/frame_swap_message_queue.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_RENDERER_GPU_FRAME_SWAP_MESSAGE_QUEUE_H_
 #define CONTENT_RENDERER_GPU_FRAME_SWAP_MESSAGE_QUEUE_H_
 
 #include <map>
 #include <memory>
 #include <vector>
 
 #include "base/auto_reset.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
 #include "cc/output/swap_promise.h"
 #include "content/common/content_export.h"
 #include "content/renderer/message_delivery_policy.h"
 
 namespace IPC {
 class Message;
 };
 
 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:
   class CONTENT_EXPORT SendMessageScope {
    public:
     virtual ~SendMessageScope() {}
   };
 
   FrameSwapMessageQueue();
 
@@ skipping 47 matching lines @@
   // threads (impl/main) are scheduled in the right order on the IO threads.
   //
   // Returns an object that must be kept in scope till an IPC message containing
   // |messages| is sent.
   std::unique_ptr<SendMessageScope> AcquireSendMessageScope();
 
   static void TransferMessages(
       std::vector<std::unique_ptr<IPC::Message>>* source,
       std::vector<IPC::Message>* dest);
 
+  uint32_t AllocateFrameToken();
+
  private:
   friend class base::RefCountedThreadSafe<FrameSwapMessageQueue>;
 
   FrameSwapMessageSubQueue* GetSubQueue(MessageDeliveryPolicy policy);
 
   ~FrameSwapMessageQueue();
 
   mutable base::Lock lock_;
   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);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_GPU_FRAME_SWAP_MESSAGE_QUEUE_H_