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

cc/resources/rasterizer.cc

 // 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.
 
 #include "cc/resources/rasterizer.h"
 
 #include <algorithm>
 
 namespace cc {
 
+RasterCanvas::~RasterCanvas() {
+}
+
+RasterCanvas::RasterCanvas() : locked_canvas_(NULL) {
+}
+
 RasterizerTask::RasterizerTask() : did_schedule_(false), did_complete_(false) {}
 
 RasterizerTask::~RasterizerTask() {
   // Debugging CHECKs to help track down a use-after-free.
   CHECK(!did_schedule_);
   CHECK(!did_run_ || did_complete_);
 }
 
 ImageDecodeTask* RasterizerTask::AsImageDecodeTask() { return NULL; }
 
@@ skipping 49 matching lines @@
   std::swap(required_for_activation_count,
             other->required_for_activation_count);
 }
 
 void RasterTaskQueue::Reset() {
   required_for_activation_count = 0u;
   items.clear();
 }
 
 }  // namespace cc