Drop frontbuffers with ui-use-gpu-process, synchronized with browser, decoupled from backbuffer dro…

ui/compositor/compositor.h

 // Copyright (c) 2012 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 UI_COMPOSITOR_COMPOSITOR_H_
 #define UI_COMPOSITOR_COMPOSITOR_H_
 #pragma once
 
 #include "base/hash_tables.h"
 #include "base/memory/ref_counted.h"
@@ skipping 173 matching lines @@
   // Compositor does not own observers. It is the responsibility of the
   // observer to remove itself when it is done observing.
   void AddObserver(CompositorObserver* observer);
   void RemoveObserver(CompositorObserver* observer);
   bool HasObserver(CompositorObserver* observer);
 
   // Returns whether a draw is pending, that is, if we're between the Draw call
   // and the OnCompositingEnded.
   bool DrawPending() const { return swap_posted_; }
 
+  bool CurrentlyCompositing() const { return currently_compositing_; }
+
   // Internal functions, called back by command-buffer contexts on swap buffer
   // events.
 
   // Signals swap has been posted.
   void OnSwapBuffersPosted();
 
   // Signals swap has completed.
   void OnSwapBuffersComplete();
 
   // Signals swap has aborted (e.g. lost context).
@@ skipping 30 matching lines @@
   ObserverList<CompositorObserver> observer_list_;
 
   gfx::AcceleratedWidget widget_;
   WebKit::WebLayer root_web_layer_;
   WebKit::WebLayerTreeView host_;
 
   // This is set to true when the swap buffers has been posted and we're waiting
   // for completion.
   bool swap_posted_;
 
+  // This is true between OnCompositingStarted and OnCompositingEnded
+  bool currently_compositing_;
+
   // The device scale factor of the monitor that this compositor is compositing
   // layers on.
   float device_scale_factor_;
 };
 
 }  // namespace ui
 
 #endif  // UI_COMPOSITOR_COMPOSITOR_H_