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

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index e0e09b5d630c48532175ed6f7c0177344743c140..543a74c330700f868890b45ac2aa5da2a50b93a9 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -215,11 +215,11 @@ void Layer::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 {
@@ -1195,7 +1195,7 @@ void Layer::PushPropertiesTo(LayerImpl* layer) {
   layer_property_changed_ = false;
   inputs_.update_rect = gfx::Rect();
 
-  layer_tree_host()->RemoveLayerShouldPushProperties(this);
+  layer_tree_host_->layer_tree()->RemoveLayerShouldPushProperties(this);
 }
 
 void Layer::TakeCopyRequests(