cc: Address comments for https://codereview.chromium.org/1287043002/

cc/trees/single_thread_proxy.cc

 // 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.
 
 #include "cc/trees/single_thread_proxy.h"
 
 #include "base/auto_reset.h"
 #include "base/profiler/scoped_tracker.h"
 #include "base/trace_event/trace_event.h"
 #include "cc/debug/benchmark_instrumentation.h"
@@ skipping 132 matching lines @@
   DCHECK(Proxy::IsMainThread());
   DCHECK(layer_tree_host_->output_surface_lost());
   output_surface_creation_callback_.Cancel();
   if (output_surface_creation_requested_)
     return;
   output_surface_creation_requested_ = true;
   layer_tree_host_->RequestNewOutputSurface();
 }
 
 scoped_ptr<OutputSurface> SingleThreadProxy::ReleaseOutputSurface() {
+  // |layer_tree_host_| should already be aware of this.
+  DCHECK(layer_tree_host_->output_surface_lost());
+
   if (scheduler_on_impl_thread_)
     scheduler_on_impl_thread_->DidLoseOutputSurface();
   return layer_tree_host_impl_->ReleaseOutputSurface();
 }
 
 void SingleThreadProxy::SetOutputSurface(
     scoped_ptr<OutputSurface> output_surface) {
   DCHECK(Proxy::IsMainThread());
   DCHECK(layer_tree_host_->output_surface_lost());
   DCHECK(output_surface_creation_requested_);
@@ skipping 745 matching lines @@
       << "DidFinishImplFrame called while not inside an impl frame!";
   inside_impl_frame_ = false;
 #endif
 }
 
 void SingleThreadProxy::SendBeginFramesToChildren(const BeginFrameArgs& args) {
   layer_tree_host_->SendBeginFramesToChildren(args);
 }
 
 }  // namespace cc