cc: fix another data race in RenderingStatsInstrumentation.

cc/debug/rendering_stats_instrumentation.h

 // 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.
 
 #ifndef CC_DEBUG_RENDERING_STATS_INSTRUMENTATION_H_
 #define CC_DEBUG_RENDERING_STATS_INSTRUMENTATION_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "base/synchronization/lock.h"
 #include "cc/debug/rendering_stats.h"
 
 namespace cc {
 
 // RenderingStatsInstrumentation is shared among threads and manages conditional
 // recording of rendering stats into a private RenderingStats instance.
 class CC_EXPORT RenderingStatsInstrumentation {
  public:
   static scoped_ptr<RenderingStatsInstrumentation> Create();
   virtual ~RenderingStatsInstrumentation();
 
-  // Return current main thread rendering stats.
-  const MainThreadRenderingStats& main_thread_rendering_stats() {
-    return main_stats_;
-  }
-  // Return current impl thread rendering stats.
-  const ImplThreadRenderingStats& impl_thread_rendering_stats() {
-    return impl_stats_;
-  }
+  // Return copy of current main thread rendering stats.
+  MainThreadRenderingStats main_thread_rendering_stats();
+
+  // Return copy of current impl thread rendering stats.
+  ImplThreadRenderingStats impl_thread_rendering_stats();
+
   // Return the accumulated, combined rendering stats.
   RenderingStats GetRenderingStats();
 
   // Add current main thread rendering stats to accumulator and
   // clear current stats.
   void AccumulateAndClearMainThreadStats();
+
   // Add current impl thread rendering stats to accumulator and
   // clear current stats.
   void AccumulateAndClearImplThreadStats();
 
   // Read and write access to the record_rendering_stats_ flag is not locked to
   // improve performance. The flag is commonly turned off and hardly changes
   // it's value during runtime.
   bool record_rendering_stats() const { return record_rendering_stats_; }
   void set_record_rendering_stats(bool record_rendering_stats) {
     if (record_rendering_stats_ != record_rendering_stats)
@@ skipping 24 matching lines @@
   bool record_rendering_stats_;
 
   base::Lock lock_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderingStatsInstrumentation);
 };
 
 }  // namespace cc
 
 #endif  // CC_DEBUG_RENDERING_STATS_INSTRUMENTATION_H_