cc: Ensure members needed on task completion get called on valid thread.

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"
 
 namespace cc {
 
 class CC_EXPORT TileTask : public Task {
  public:
   typedef std::vector<scoped_refptr<TileTask>> Vector;
 
+  struct TaskCompletionInfo {};
+
   const TileTask::Vector& dependencies() const { return dependencies_; }
 
   // Indicates whether this TileTask can be run at the same time as other tasks
   // 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_;
   }
 
   virtual void OnTaskCompleted() = 0;
 
  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_;
 };
 
 }  // namespace cc
 
 #endif  // CC_RASTER_TILE_TASK_H_