Do not give GPU memory to backgrounded compositors.

cc/test/fake_output_surface_client.cc

 // Copyright 2013 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.
 
 #include "cc/test/fake_output_surface_client.h"
 
 namespace cc {
 
 bool FakeOutputSurfaceClient::DeferredInitialize(
     scoped_refptr<ContextProvider> offscreen_context_provider) {
   deferred_initialize_called_ = true;
   return deferred_initialize_result_;
 }
 
 void FakeOutputSurfaceClient::BeginImplFrame(const BeginFrameArgs& args) {
   begin_impl_frame_count_++;
 }
 
 void FakeOutputSurfaceClient::DidLoseOutputSurface() {
   did_lose_output_surface_called_ = true;
 }
 
 void FakeOutputSurfaceClient::SetMemoryPolicy(
     const ManagedMemoryPolicy& policy) {
   memory_policy_ = policy;
 }
 
-void FakeOutputSurfaceClient::SetDiscardBackBufferWhenNotVisible(bool discard) {
-  discard_backbuffer_when_not_visible_ = discard;
-}
-
-
 }  // namespace cc