Mac: Fix black flashing during tab switch

content/browser/compositor/browser_compositor_view_mac.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_BROWSER_COMPOSITOR_VIEW_MAC_H_
 #define CONTENT_BROWSER_COMPOSITOR_BROWSER_COMPOSITOR_VIEW_MAC_H_
 
 #include "ui/accelerated_widget_mac/accelerated_widget_mac.h"
 #include "ui/compositor/compositor.h"
+#include "ui/compositor/compositor_observer.h"
 
 namespace content {
 
 // A ui::Compositor and a gfx::AcceleratedWidget (and helper) that it draws
 // into. This structure is used to efficiently recycle these structures across
 // tabs (because creating a new ui::Compositor for each tab would be expensive
 // in terms of time and resources).
-class BrowserCompositorMac {
+class BrowserCompositorMac : public ui::CompositorObserver {
  public:
-  ~BrowserCompositorMac();
+  virtual ~BrowserCompositorMac();
 
   // Create a compositor, or recycle a preexisting one.
   static scoped_ptr<BrowserCompositorMac> Create();
 
   // Delete a compositor, or allow it to be recycled.
   static void Recycle(scoped_ptr<BrowserCompositorMac> compositor);
 
   // Indicate that the recyclable compositor should be destroyed, and no future
   // compositors should be recycled.
   static void DisableRecyclingForShutdown();
 
   ui::Compositor* compositor() { return &compositor_; }
   ui::AcceleratedWidgetMac* accelerated_widget_mac() {
     return accelerated_widget_mac_.get();
   }
 
   // Suspend will prevent the compositor from producing new frames. This should
   // be called to avoid creating spurious frames while changing state.
   // Compositors are created as suspended.
   void Suspend();
   void Unsuspend();
 
  private:
   BrowserCompositorMac();
 
+  // ui::CompositorObserver implementation:
+  void OnCompositingDidCommit(ui::Compositor* compositor) override;
+  void OnCompositingStarted(ui::Compositor* compositor,
+                            base::TimeTicks start_time) override {}
+  void OnCompositingEnded(ui::Compositor* compositor) override {}
+  void OnCompositingAborted(ui::Compositor* compositor) override {}
+  void OnCompositingLockStateChanged(ui::Compositor* compositor) override {}
+  void OnCompositingShuttingDown(ui::Compositor* compositor) override {}
+
   scoped_ptr<ui::AcceleratedWidgetMac> accelerated_widget_mac_;
   ui::Compositor compositor_;
   scoped_refptr<ui::CompositorLock> compositor_suspended_lock_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserCompositorMac);
 };
 
 // A class to keep around whenever a BrowserCompositorMac may be created.
 // While at least one instance of this class exists, a spare
 // BrowserCompositorViewCocoa will be kept around to be recycled so that the
 // next BrowserCompositorMac to be created will be be created quickly.
 class BrowserCompositorMacPlaceholder {
  public:
   BrowserCompositorMacPlaceholder();
   ~BrowserCompositorMacPlaceholder();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(BrowserCompositorMacPlaceholder);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_COMPOSITOR_BROWSER_COMPOSITOR_VIEW_MAC_H_