Do not give GPU memory to backgrounded compositors.

cc/output/software_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_SOFTWARE_RENDERER_H_
 #define CC_OUTPUT_SOFTWARE_RENDERER_H_
 
 #include "base/basictypes.h"
 #include "cc/base/cc_export.h"
 #include "cc/output/compositor_frame.h"
@@ skipping 27 matching lines @@
   virtual void Finish() OVERRIDE;
   virtual void SwapBuffers() OVERRIDE;
   virtual void GetFramebufferPixels(void* pixels, gfx::Rect rect) OVERRIDE;
   virtual void SetVisible(bool visible) OVERRIDE;
   virtual void SendManagedMemoryStats(
       size_t bytes_visible,
       size_t bytes_visible_and_nearby,
       size_t bytes_allocated) OVERRIDE  {}
   virtual void ReceiveSwapBuffersAck(
       const CompositorFrameAck& ack) OVERRIDE;
-  virtual void SetDiscardBackBufferWhenNotVisible(bool discard) OVERRIDE;
   virtual void DiscardBackbuffer() OVERRIDE;
   virtual void EnsureBackbuffer() OVERRIDE;
 
  protected:
   virtual void BindFramebufferToOutputSurface(DrawingFrame* frame) OVERRIDE;
   virtual bool BindFramebufferToTexture(
       DrawingFrame* frame,
       const ScopedResource* texture,
       gfx::Rect target_rect) OVERRIDE;
   virtual void SetDrawViewport(gfx::Rect window_space_viewport) OVERRIDE;
@@ skipping 52 matching lines @@
   scoped_ptr<ResourceProvider::ScopedWriteLockSoftware>
       current_framebuffer_lock_;
   scoped_ptr<SoftwareFrameData> current_frame_data_;
 
   DISALLOW_COPY_AND_ASSIGN(SoftwareRenderer);
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_SOFTWARE_RENDERER_H_