cc: Make async readback path use async glRreadPixels.

cc/resources/resource_provider.h

 // Copyright 2012 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.
 
 #ifndef CC_RESOURCES_RESOURCE_PROVIDER_H_
 #define CC_RESOURCES_RESOURCE_PROVIDER_H_
 
 #include <deque>
 #include <set>
 #include <string>
@@ skipping 109 matching lines @@
   size_t NumBlockingUploads();
   void MarkPendingUploadsAsNonBlocking();
   double EstimatedUploadsPerSecond();
   void FlushUploads();
   void ReleaseCachedData();
 
   // Flush all context operations, kicking uploads and ensuring ordering with
   // respect to other contexts.
   void Flush();
 
+  // Finish all context operations, causing any pending callbacks to be
+  // scheduled.
+  void Finish();
+
   // Only flush the command buffer if supported.
   // Returns true if the shallow flush occurred, false otherwise.
   bool ShallowFlushIfSupported();
 
   // Creates accounting for a child. Returns a child ID.
   int CreateChild();
 
   // Destroys accounting for the child, deleting all accounted resources.
   void DestroyChild(int child);
 
@@ skipping 261 matching lines @@
   base::ThreadChecker thread_checker_;
 
   scoped_refptr<Fence> current_read_lock_fence_;
 
   DISALLOW_COPY_AND_ASSIGN(ResourceProvider);
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_RESOURCE_PROVIDER_H_