Do not give GPU memory to backgrounded compositors.

cc/output/renderer.h

 // Copyright 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 CC_OUTPUT_RENDERER_H_
 #define CC_OUTPUT_RENDERER_H_
 
 #include "base/basictypes.h"
 #include "cc/base/cc_export.h"
 #include "cc/quads/render_pass.h"
@@ skipping 54 matching lines @@
   virtual void GetFramebufferPixels(void* pixels, gfx::Rect rect) = 0;
 
   virtual bool IsContextLost();
 
   virtual void SetVisible(bool visible) = 0;
 
   virtual void SendManagedMemoryStats(size_t bytes_visible,
                                       size_t bytes_visible_and_nearby,
                                       size_t bytes_allocated) = 0;
 
-  virtual void SetDiscardBackBufferWhenNotVisible(bool discard) = 0;
-
  protected:
   explicit Renderer(RendererClient* client, const LayerTreeSettings* settings)
       : client_(client), settings_(settings) {}
 
   RendererClient* client_;
   const LayerTreeSettings* settings_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(Renderer);
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_RENDERER_H_