Fix race conditions in window snapshot code.

cc/trees/layer_tree_host_impl.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/layer_tree_host_impl.h"
 
 #include <algorithm>
 
 #include "base/basictypes.h"
 #include "base/containers/hash_tables.h"
@@ skipping 1219 matching lines @@
 static void LayerTreeHostImplDidBeginTracingCallback(LayerImpl* layer) {
   layer->DidBeginTracing();
 }
 
 void LayerTreeHostImpl::DrawLayers(FrameData* frame,
                                    base::TimeTicks frame_begin_time) {
   TRACE_EVENT0("cc", "LayerTreeHostImpl::DrawLayers");
   DCHECK(CanDraw());
 
   if (frame->has_no_damage) {
+    LOG(INFO) << "EarlyOut_NoDamage";
     TRACE_EVENT0("cc", "EarlyOut_NoDamage");
     DCHECK(!output_surface_->capabilities()
                .draw_and_swap_full_viewport_every_frame);
     return;
   }
 
   DCHECK(!frame->render_passes.empty());
 
   int old_dropped_frame_count = fps_counter_->dropped_frame_count();
   fps_counter_->SaveTimeStamp(frame_begin_time,
@@ skipping 1327 matching lines @@
 
 ResourceProvider::ResourceId LayerTreeHostImpl::ResourceIdForUIResource(
     UIResourceId uid) const {
   UIResourceMap::const_iterator iter = ui_resource_map_.find(uid);
   if (iter != ui_resource_map_.end())
     return iter->second;
   return 0;
 }
 
 }  // namespace cc