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

cc/layers/layer.cc

 // Copyright 2010 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/layers/layer.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 197 matching lines @@
 
 void Layer::SetNextCommitWaitsForActivation() {
   if (!layer_tree_host_)
     return;
 
   layer_tree_host_->SetNextCommitWaitsForActivation();
 }
 
 void Layer::SetNeedsPushProperties() {
   if (layer_tree_host_)
-    layer_tree_host_->AddLayerShouldPushProperties(this);
+    layer_tree_host_->layer_tree()->AddLayerShouldPushProperties(this);

[Khushal, 2016/07/18 16:59:32]

I would suggest add a public method to Layer to access the LayerTree.

LayerTree* GetLayerTree() const {
  return layer_tree_host_ ? layer_tree_host_->layer_tree() : nullptr;
}

And then you can start moving the call sites to use the layer tree as you move
functionalities there. This way when you finally change Layer::SetLayerTreeHost
to Layer::SetLayerTree, you won't have to change all the call sites.

[xingliu, 2016/07/19 22:47:37]

Done. Good idea.

 }
 
 void Layer::ResetNeedsPushPropertiesForTesting() {
-  layer_tree_host_->RemoveLayerShouldPushProperties(this);
+  layer_tree_host_->layer_tree()->RemoveLayerShouldPushProperties(this);
 }
 
 bool Layer::IsPropertyChangeAllowed() const {
   if (!layer_tree_host_)
     return true;
 
   return !layer_tree_host_->in_paint_layer_contents();
 }
 
 sk_sp<SkPicture> Layer::GetPicture() const {
@@ skipping 955 matching lines @@
   layer->SetUpdateRect(inputs_.update_rect);
 
   layer->SetHasWillChangeTransformHint(has_will_change_transform_hint());
   layer->SetNeedsPushProperties();
 
   // Reset any state that should be cleared for the next update.
   subtree_property_changed_ = false;
   layer_property_changed_ = false;
   inputs_.update_rect = gfx::Rect();
 
-  layer_tree_host()->RemoveLayerShouldPushProperties(this);
+  layer_tree_host_->layer_tree()->RemoveLayerShouldPushProperties(this);
 }
 
 void Layer::TakeCopyRequests(
     std::vector<std::unique_ptr<CopyOutputRequest>>* requests) {
   for (auto& it : inputs_.copy_requests) {
     scoped_refptr<base::SingleThreadTaskRunner> main_thread_task_runner =
         layer_tree_host()->task_runner_provider()->MainThreadTaskRunner();
     std::unique_ptr<CopyOutputRequest> original_request = std::move(it);
     const CopyOutputRequest& original_request_ref = *original_request;
     std::unique_ptr<CopyOutputRequest> main_thread_request =
@@ skipping 634 matching lines @@
       ->num_copy_requests_in_subtree;
 }
 
 gfx::Transform Layer::screen_space_transform() const {
   DCHECK_NE(transform_tree_index_, -1);
   return draw_property_utils::ScreenSpaceTransform(
       this, layer_tree_host_->property_trees()->transform_tree);
 }
 
 }  // namespace cc