Do not give GPU memory to backgrounded compositors.

cc/trees/layer_tree_host_impl.h

 // Copyright 2011 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 CC_TREES_LAYER_TREE_HOST_IMPL_H_
 #define CC_TREES_LAYER_TREE_HOST_IMPL_H_
 
 #include <list>
 #include <set>
 #include <string>
@@ skipping 212 matching lines @@
   virtual void BeginImplFrame(const BeginFrameArgs& args) OVERRIDE;
   virtual void SetExternalDrawConstraints(
       const gfx::Transform& transform,
       gfx::Rect viewport,
       gfx::Rect clip,
       bool valid_for_tile_management) OVERRIDE;
   virtual void DidLoseOutputSurface() OVERRIDE;
   virtual void OnSwapBuffersComplete() OVERRIDE;
   virtual void ReclaimResources(const CompositorFrameAck* ack) OVERRIDE;
   virtual void SetMemoryPolicy(const ManagedMemoryPolicy& policy) OVERRIDE;
-  virtual void SetDiscardBackBufferWhenNotVisible(bool discard) OVERRIDE;
   virtual void SetTreeActivationCallback(const base::Closure& callback)
       OVERRIDE;
 
   // Called from LayerTreeImpl.
   void OnCanDrawStateChangedForTree();
 
   // Implementation.
   bool CanDraw() const;
   OutputSurface* output_surface() const { return output_surface_.get(); }
 
@@ skipping 381 matching lines @@
   base::Closure tree_activation_callback_;
 
   SharedBitmapManager* shared_bitmap_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_TREES_LAYER_TREE_HOST_IMPL_H_