cc: Fix data race in cc::TaskState::IsFinished.

cc/raster/tile_task.h

 // Copyright 2014 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_RASTER_TILE_TASK_H_
 #define CC_RASTER_TILE_TASK_H_
 
 #include <vector>
 
 #include "cc/raster/task.h"
@@ skipping 10 matching lines @@
   // in the task graph. If false, this task will be scheduled with
   // TASK_CATEGORY_NONCONCURRENT_FOREGROUND.
   bool supports_concurrent_execution() const {
     return supports_concurrent_execution_;
   }
 
   // This function should be called from origin thread to process the completion
   // of the task.
   virtual void OnTaskCompleted() = 0;
 
+  void DidComplete();
+  bool HasCompleted() const;
+
  protected:
   explicit TileTask(bool supports_concurrent_execution);
   TileTask(bool supports_concurrent_execution, TileTask::Vector* dependencies);
   ~TileTask() override;
 
   const bool supports_concurrent_execution_;
   TileTask::Vector dependencies_;
+  bool did_complete_;
 };
 
 }  // namespace cc
 
 #endif  // CC_RASTER_TILE_TASK_H_