Do not give GPU memory to backgrounded compositors.

cc/output/output_surface.cc

 // Copyright (c) 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/output/output_surface.h"
 
 #include <algorithm>
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 471 matching lines @@
   pending_gpu_latency_query_ids_.push_back(gpu_latency_query_id);
 }
 
 void OutputSurface::PostSwapBuffersComplete() {
   base::MessageLoop::current()->PostTask(
       FROM_HERE,
       base::Bind(&OutputSurface::OnSwapBuffersComplete,
                  weak_ptr_factory_.GetWeakPtr()));
 }
 
-void OutputSurface::SetMemoryPolicy(const ManagedMemoryPolicy& policy,
-                                    bool discard_backbuffer) {
-  TRACE_EVENT2("cc", "OutputSurface::SetMemoryPolicy",
-               "bytes_limit_when_visible", policy.bytes_limit_when_visible,
-               "discard_backbuffer", discard_backbuffer);
+void OutputSurface::SetMemoryPolicy(const ManagedMemoryPolicy& policy) {
+  TRACE_EVENT1("cc", "OutputSurface::SetMemoryPolicy",
+               "bytes_limit_when_visible", policy.bytes_limit_when_visible);
   // Just ignore the memory manager when it says to set the limit to zero
   // bytes. This will happen when the memory manager thinks that the renderer
   // is not visible (which the renderer knows better).
   if (policy.bytes_limit_when_visible)
     client_->SetMemoryPolicy(policy);
-  client_->SetDiscardBackBufferWhenNotVisible(discard_backbuffer);
 }
 
 }  // namespace cc