Introduce separate client and init path for single-threaded cc

cc/trees/layer_tree_host_unittest_scroll.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 "cc/trees/layer_tree_host.h"
 
 #include "base/memory/weak_ptr.h"
 #include "cc/layers/content_layer.h"
 #include "cc/layers/layer.h"
 #include "cc/layers/layer_impl.h"
@@ skipping 994 matching lines @@
   ASSERT_TRUE(impl_thread.Start());
 
   bool received_stop_flinging = false;
   LayerTreeSettings settings;
 
   ThreadCheckingInputHandlerClient input_handler_client(
           impl_thread.message_loop_proxy().get(), &received_stop_flinging);
   FakeLayerTreeHostClient client(FakeLayerTreeHostClient::DIRECT_3D);
 
   ASSERT_TRUE(impl_thread.message_loop_proxy().get());
-  scoped_ptr<LayerTreeHost> layer_tree_host = LayerTreeHost::Create(
+  scoped_ptr<LayerTreeHost> layer_tree_host = LayerTreeHost::CreateThreaded(
       &client, NULL, settings, impl_thread.message_loop_proxy());
 
   impl_thread.message_loop_proxy()
       ->PostTask(FROM_HERE,
                  base::Bind(&BindInputHandlerOnCompositorThread,
                             layer_tree_host->GetInputHandler(),
                             base::Unretained(&input_handler_client)));
 
   layer_tree_host->DidStopFlinging();
   layer_tree_host.reset();
@@ skipping 90 matching lines @@
     RunTest(true, false, false);
 }
 
 TEST_F(LayerTreeHostScrollTestLayerStructureChange, ScrollDestroyWholeTree) {
     scroll_destroy_whole_tree_ = true;
     RunTest(true, false, false);
 }
 
 }  // namespace
 }  // namespace cc