cc: Parameterize the main thread task runner

cc/layers/scrollbar_layer_unittest.cc

 // 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.
 
 #include "base/containers/hash_tables.h"
 #include "cc/animation/scrollbar_animation_controller.h"
 #include "cc/layers/append_quads_data.h"
 #include "cc/layers/painted_scrollbar_layer.h"
 #include "cc/layers/painted_scrollbar_layer_impl.h"
 #include "cc/layers/scrollbar_layer_interface.h"
@@ skipping 556 matching lines @@
 }
 
 class MockLayerTreeHost : public LayerTreeHost {
  public:
   MockLayerTreeHost(FakeLayerTreeHostClient* client,
                     const LayerTreeSettings& settings)
       : LayerTreeHost(client, NULL, settings),
         next_id_(1),
         total_ui_resource_created_(0),
         total_ui_resource_deleted_(0) {
-    InitializeSingleThreaded(client);
+    InitializeSingleThreaded(client, base::MessageLoopProxy::current());
   }
 
   virtual UIResourceId CreateUIResource(UIResourceClient* content) OVERRIDE {
     total_ui_resource_created_++;
     UIResourceId nid = next_id_++;
     ui_resource_bitmap_map_.insert(
         std::make_pair(nid, content->GetBitmap(nid, false)));
     return nid;
   }
 
@@ skipping 305 matching lines @@
   TestScale(gfx::Rect(1240, 0, 15, 1333), 2.7754839f);
   TestScale(gfx::Rect(1240, 0, 15, 677), 2.46677136f);
 
   // Horizontal Scrollbars.
   TestScale(gfx::Rect(0, 1240, 1333, 15), 2.7754839f);
   TestScale(gfx::Rect(0, 1240, 677, 15), 2.46677136f);
 }
 
 }  // namespace
 }  // namespace cc