Introduce separate client and init path for single-threaded cc

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 494 matching lines @@
   scoped_ptr<TestWebGraphicsContext3D> context =
       TestWebGraphicsContext3D::Create();
   int max_size = 0;
   context->getIntegerv(GL_MAX_TEXTURE_SIZE, &max_size);
   SetScrollbarBounds(gfx::Size(max_size + 100, max_size + 100));
   RunTest(true, true, true);
 }
 
 class MockLayerTreeHost : public LayerTreeHost {
  public:
-  MockLayerTreeHost(LayerTreeHostClient* client,
+  MockLayerTreeHost(FakeLayerTreeHostClient* client,
                     const LayerTreeSettings& settings)
       : LayerTreeHost(client, NULL, settings),
         next_id_(1),
         total_ui_resource_created_(0),
         total_ui_resource_deleted_(0) {
-    Initialize(NULL);
+    InitializeSingleThreaded(client);
   }
 
   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 197 matching lines @@
 TEST_F(ScaledScrollbarLayerTestResourceCreation, ScaledResourceUpload) {
   // Pick a test scale that moves the scrollbar's (non-zero) position to
   // a non-pixel-aligned location.
   TestResourceUpload(.041f);
   TestResourceUpload(1.41f);
   TestResourceUpload(4.1f);
 }
 
 }  // namespace
 }  // namespace cc