cc: Implement shared worker contexts. (v1)

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 32 matching lines @@
     TRACE_EVENT0("cc", "RasterBufferImpl::Playback");
     // GPU raster doesn't do low res tiles, so should always include images.
     DCHECK(include_images);
     ContextProvider* context_provider = rasterizer_->resource_provider()
                                             ->output_surface()
                                             ->worker_context_provider();
     DCHECK(context_provider);
 
     ContextProvider::ScopedContextLock scoped_context(context_provider);
 
+    gpu::gles2::GLES2Interface* gl = scoped_context.ContextGL();
+    if (!gl)
+      return;
+
     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.
-    scoped_context.ContextGL()->OrderingBarrierCHROMIUM();
+    gl->OrderingBarrierCHROMIUM();
   }
 
  private:
   GpuRasterizer* rasterizer_;
   ResourceProvider::ScopedWriteLockGr lock_;
   bool resource_has_previous_content_;
 
   DISALLOW_COPY_AND_ASSIGN(RasterBufferImpl);
 };
 
@@ skipping 160 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