Re-land: cc: Use worker context for one-copy tile initialization.

cc/raster/gpu_tile_task_worker_pool.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/raster/gpu_tile_task_worker_pool.h"
 
 #include <algorithm>
 
 #include "base/trace_event/trace_event.h"
 #include "cc/playback/raster_source.h"
@@ skipping 25 matching lines @@
   // Overridden from RasterBuffer:
   void Playback(const RasterSource* raster_source,
                 const gfx::Rect& raster_full_rect,
                 const gfx::Rect& raster_dirty_rect,
                 uint64_t new_content_id,
                 float scale) override {
     TRACE_EVENT0("cc", "RasterBufferImpl::Playback");
     ContextProvider* context_provider = rasterizer_->resource_provider()
                                             ->output_surface()
                                             ->worker_context_provider();
+    DCHECK(context_provider);
 
-    // The context lock must be held while accessing the context on a
-    // worker thread.
-    base::AutoLock context_lock(*context_provider->GetLock());
-
-    // Allow this worker thread to bind to context_provider.
-    context_provider->DetachFromThread();
+    ContextProvider::ScopedContextGL scoped_context(context_provider);
 
     gfx::Rect playback_rect = raster_full_rect;
     if (resource_has_previous_content_) {
       playback_rect.Intersect(raster_dirty_rect);
     }
     DCHECK(!playback_rect.IsEmpty())
         << "Why are we rastering a tile that's not dirty?";
 
     // TODO(danakj): Implement partial raster with raster_dirty_rect.
     // Rasterize source into resource.
     rasterizer_->RasterizeSource(&lock_, raster_source, raster_full_rect,
                                  playback_rect, scale);
 
     // Barrier to sync worker context output to cc context.
-    context_provider->ContextGL()->OrderingBarrierCHROMIUM();
-
-    // Allow compositor thread to bind to context_provider.
-    context_provider->DetachFromThread();
+    scoped_context.ContextGL()->OrderingBarrierCHROMIUM();
   }
 
  private:
   GpuRasterizer* rasterizer_;
   ResourceProvider::ScopedWriteLockGr lock_;
   bool resource_has_previous_content_;
 
   DISALLOW_COPY_AND_ASSIGN(RasterBufferImpl);
 };
 
@@ skipping 162 matching lines @@
 void GpuTileTaskWorkerPool::OnTaskSetFinished(TaskSet task_set) {
   TRACE_EVENT1("cc", "GpuTileTaskWorkerPool::OnTaskSetFinished", "task_set",
                task_set);
 
   DCHECK(tasks_pending_[task_set]);
   tasks_pending_[task_set] = false;
   client_->DidFinishRunningTileTasks(task_set);
 }
 
 }  // namespace cc