tracing: Make ConvertableToTraceFormat move-only scoped_ptr

cc/raster/bitmap_tile_task_worker_pool.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_BITMAP_TILE_TASK_WORKER_POOL_H_
 #define CC_RASTER_BITMAP_TILE_TASK_WORKER_POOL_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
@@ skipping 37 matching lines @@
       uint64_t resource_content_id,
       uint64_t previous_content_id) override;
   void ReleaseBufferForRaster(scoped_ptr<RasterBuffer> buffer) override;
 
  protected:
   BitmapTileTaskWorkerPool(base::SequencedTaskRunner* task_runner,
                            TaskGraphRunner* task_graph_runner,
                            ResourceProvider* resource_provider);
 
  private:
-  scoped_refptr<base::trace_event::ConvertableToTraceFormat> StateAsValue()
-      const;
+  scoped_ptr<base::trace_event::ConvertableToTraceFormat> StateAsValue() const;
 
   scoped_refptr<base::SequencedTaskRunner> task_runner_;
   TaskGraphRunner* task_graph_runner_;
   const NamespaceToken namespace_token_;
   ResourceProvider* resource_provider_;
 
   Task::Vector completed_tasks_;
 
   DISALLOW_COPY_AND_ASSIGN(BitmapTileTaskWorkerPool);
 };
 
 }  // namespace cc
 
 #endif  // CC_RASTER_BITMAP_TILE_TASK_WORKER_POOL_H_