Setup LayerTree class, refactor 2 functions from LayerTreeHost to it.

cc/trees/layer_tree_host_unittest.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_host.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 2965 matching lines @@
 class PushPropertiesCountingLayer : public Layer {
  public:
   static scoped_refptr<PushPropertiesCountingLayer> Create() {
     return new PushPropertiesCountingLayer();
   }
 
   void PushPropertiesTo(LayerImpl* layer) override {
     Layer::PushPropertiesTo(layer);
     push_properties_count_++;
     if (persist_needs_push_properties_) {
-      layer_tree_host()->AddLayerShouldPushProperties(this);
+      layer_tree_host()->GetLayerTree()->AddLayerShouldPushProperties(this);
     }
   }
 
   // Something to make this layer push properties, but no other layer.
   void MakePushProperties() { SetContentsOpaque(!contents_opaque()); }
 
   std::unique_ptr<LayerImpl> CreateLayerImpl(
       LayerTreeImpl* tree_impl) override {
     return PushPropertiesCountingLayerImpl::Create(tree_impl, id());
   }
@@ skipping 3876 matching lines @@
  private:
   FakeContentLayerClient client_;
   const gfx::Size viewport_size_;
   const gfx::Size large_image_size_;
 };
 
 SINGLE_AND_MULTI_THREAD_TEST_F(GpuRasterizationSucceedsWithLargeImage);
 
 }  // namespace
 }  // namespace cc