cc: Do bitmap conversion for RasterBuffer in the worker thread.

cc/resources/image_raster_worker_pool.cc

 // 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.
 
 #include "cc/resources/image_raster_worker_pool.h"
 
 #include "base/debug/trace_event.h"
 #include "base/debug/trace_event_argument.h"
 #include "cc/debug/traced_value.h"
 #include "cc/resources/resource.h"
@@ skipping 123 matching lines @@
 
     task->WillComplete();
     task->CompleteOnOriginThread(this);
     task->DidComplete();
 
     task->RunReplyOnOriginThread();
   }
   completed_tasks_.clear();
 }
 
-SkCanvas* ImageRasterWorkerPool::AcquireCanvasForRaster(RasterTask* task) {
+RasterCanvas* ImageRasterWorkerPool::AcquireCanvasForRaster(RasterTask* task) {
   return resource_provider_->MapImageRasterBuffer(task->resource()->id());
 }
 
 void ImageRasterWorkerPool::ReleaseCanvasForRaster(RasterTask* task) {
   resource_provider_->UnmapImageRasterBuffer(task->resource()->id());
 
   // Map/UnmapImageRasterBuffer provides direct access to the memory used by the
   // GPU. Read lock fences are required to ensure that we're not trying to map a
   // resource that is currently in-use by the GPU.
   resource_provider_->EnableReadLockFences(task->resource()->id());
@@ skipping 23 matching lines @@
 ImageRasterWorkerPool::StateAsValue() const {
   scoped_refptr<base::debug::TracedValue> state =
       new base::debug::TracedValue();
 
   state->SetBoolean("tasks_required_for_activation_pending",
                     raster_tasks_required_for_activation_pending_);
   return state;
 }
 
 }  // namespace cc