cc: Use correct message loop proxy in BlockingTaskRunner

cc/trees/layer_tree_impl.cc

 // Copyright 2011 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/trees/layer_tree_impl.h"
 
 #include <limits>
 #include <set>
 
 #include "base/debug/trace_event.h"
@@ skipping 1406 matching lines @@
 }
 
 void LayerTreeImpl::UnregisterPictureLayerImpl(PictureLayerImpl* layer) {
   layer_tree_host_impl_->UnregisterPictureLayerImpl(layer);
 }
 
 void LayerTreeImpl::InputScrollAnimationFinished() {
   layer_tree_host_impl_->ScrollEnd();
 }
 
+BlockingTaskRunner* LayerTreeImpl::BlockingMainThreadTaskRunner() const {
+  return proxy()->blocking_main_thread_task_runner();
+}
+
 }  // namespace cc