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..aafc73eb0830bfe8d8cb136b89962fb5e6180fa1 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -129,7 +129,7 @@ void Layer::SetLayerTreeHost(LayerTreeHost* host) {
   if (layer_tree_host_) {
     layer_tree_host_->property_trees()->RemoveIdFromIdToIndexMaps(id());
     layer_tree_host_->property_trees()->needs_rebuild = true;
-    layer_tree_host_->UnregisterLayer(this);
+    GetLayerTree()->UnregisterLayer(this);
     if (inputs_.element_id) {
       layer_tree_host_->animation_host()->UnregisterElement(
           inputs_.element_id, ElementListType::ACTIVE);
@@ -138,7 +138,7 @@ void Layer::SetLayerTreeHost(LayerTreeHost* host) {
   }
   if (host) {
     host->property_trees()->needs_rebuild = true;
-    host->RegisterLayer(this);
+    host->GetLayerTree()->RegisterLayer(this);
     if (inputs_.element_id) {
       host->AddToElementMap(this);
       host->animation_host()->RegisterElement(inputs_.element_id,
@@ -215,18 +215,18 @@ void Layer::SetNextCommitWaitsForActivation() {
 
 void Layer::SetNeedsPushProperties() {
   if (layer_tree_host_)
-    layer_tree_host_->AddLayerShouldPushProperties(this);
+    GetLayerTree()->AddLayerShouldPushProperties(this);
 }
 
 void Layer::ResetNeedsPushPropertiesForTesting() {
-  layer_tree_host_->RemoveLayerShouldPushProperties(this);
+  GetLayerTree()->RemoveLayerShouldPushProperties(this);
 }
 
 bool Layer::IsPropertyChangeAllowed() const {
   if (!layer_tree_host_)
     return true;
 
-  return !layer_tree_host_->in_paint_layer_contents();
+  return !GetLayerTree()->in_paint_layer_contents();
 }
 
 sk_sp<SkPicture> Layer::GetPicture() const {
@@ -1195,7 +1195,7 @@ void Layer::PushPropertiesTo(LayerImpl* layer) {
   layer_property_changed_ = false;
   inputs_.update_rect = gfx::Rect();
 
-  layer_tree_host()->RemoveLayerShouldPushProperties(this);
+  GetLayerTree()->RemoveLayerShouldPushProperties(this);
 }
 
 void Layer::TakeCopyRequests(
@@ -1247,7 +1247,7 @@ void Layer::ClearLayerTreePropertiesForDeserializationAndAddToMap(
   (*layer_map)[inputs_.layer_id] = this;
 
   if (layer_tree_host_)
-    layer_tree_host_->UnregisterLayer(this);
+    GetLayerTree()->UnregisterLayer(this);
 
   layer_tree_host_ = nullptr;
   parent_ = nullptr;
@@ -1285,7 +1285,7 @@ void Layer::FromLayerNodeProto(const proto::LayerNode& proto,
   inputs_.layer_id = proto.id();
 
   layer_tree_host_ = layer_tree_host;
-  layer_tree_host_->RegisterLayer(this);
+  GetLayerTree()->RegisterLayer(this);
 
   for (int i = 0; i < proto.children_size(); ++i) {
     const proto::LayerNode& child_proto = proto.children(i);
@@ -1747,7 +1747,8 @@ void Layer::SetHasWillChangeTransformHint(bool has_will_change) {
 }
 
 AnimationHost* Layer::GetAnimationHost() const {
-  return layer_tree_host_ ? layer_tree_host_->animation_host() : nullptr;
+  LayerTree* layer_tree = GetLayerTree();
+  return layer_tree ? layer_tree->animation_host() : nullptr;
 }
 
 ElementListType Layer::GetElementTypeForAnimation() const {
@@ -1849,4 +1850,8 @@ gfx::Transform Layer::screen_space_transform() const {
       this, layer_tree_host_->property_trees()->transform_tree);
 }
 
+LayerTree* Layer::GetLayerTree() const {
+  return layer_tree_host_ ? layer_tree_host_->GetLayerTree() : nullptr;
+}
+
 }  // namespace cc