De-dupe copy requests for tab capture in DelegatedFrameHost.

content/browser/compositor/delegated_frame_host.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_BROWSER_COMPOSITOR_DELEGATED_FRAME_HOST_H_
 #define CONTENT_BROWSER_COMPOSITOR_DELEGATED_FRAME_HOST_H_
 
 #include "cc/layers/delegated_frame_provider.h"
 #include "cc/layers/delegated_frame_resource_collection.h"
 #include "cc/output/copy_output_result.h"
@@ skipping 290 matching lines @@
     NO_PENDING_COMMIT,
   };
   CanLockCompositorState can_lock_compositor_;
 
   base::TimeTicks last_draw_ended_;
 
   // Subscriber that listens to frame presentation events.
   scoped_ptr<RenderWidgetHostViewFrameSubscriber> frame_subscriber_;
   std::vector<scoped_refptr<OwnedMailbox> > idle_frame_subscriber_textures_;
 
+  // Set to true if a frame was received from the renderer and a copy request
+  // was made for the frame subscriber, but drawing has not yet started.  This
+  // is used to prevent more than one copy request being executed per draw.
+  bool frame_subscriber_copy_request_pending_;
+
   // Callback used to pass the output request to the layer or to a function
   // specified by a test.
   base::Callback<void(scoped_ptr<cc::CopyOutputRequest>)>
       request_copy_of_output_callback_for_testing_;
 
   // YUV readback pipeline.
   scoped_ptr<content::ReadbackYUVInterface>
       yuv_readback_pipeline_;
 
   scoped_ptr<DelegatedFrameEvictor> delegated_frame_evictor_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_COMPOSITOR_DELEGATED_FRAME_HOST_H_