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

cc/resources/gpu_raster_worker_pool.cc

Index: cc/resources/gpu_raster_worker_pool.cc
diff --git a/cc/resources/gpu_raster_worker_pool.cc b/cc/resources/gpu_raster_worker_pool.cc
index f38fa7b14a1acb22bcd8004fd4e12d73191d7c97..3c3ecbd18e20d89b0ce972e5077663f9daa2baed 100644
--- a/cc/resources/gpu_raster_worker_pool.cc
+++ b/cc/resources/gpu_raster_worker_pool.cc
@@ -148,11 +148,11 @@ void GpuRasterWorkerPool::CheckForCompletedTasks() {
   completed_tasks_.clear();
 }
 
-SkCanvas* GpuRasterWorkerPool::AcquireCanvasForRaster(RasterTask* task) {
+RasterBuffer* GpuRasterWorkerPool::AcquireBufferForRaster(RasterTask* task) {
   return resource_provider_->MapGpuRasterBuffer(task->resource()->id());
 }
 
-void GpuRasterWorkerPool::ReleaseCanvasForRaster(RasterTask* task) {
+void GpuRasterWorkerPool::ReleaseBufferForRaster(RasterTask* task) {
   resource_provider_->UnmapGpuRasterBuffer(task->resource()->id());
 }