Refactor MutatorHostClient from LayerTreeHost to LayerTree.

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index 6f9239a1940986f39d024f5003f8ac7a8afc1f4d..400cc48029e93e99145d02c0d171ac094bc93879 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -135,14 +135,14 @@ void Layer::SetLayerTreeHost(LayerTreeHost* host) {
     if (inputs_.element_id) {
       layer_tree_host_->animation_host()->UnregisterElement(
           inputs_.element_id, ElementListType::ACTIVE);
-      layer_tree_host_->RemoveFromElementMap(this);
+      layer_tree_->RemoveFromElementMap(this);
     }
   }
   if (host) {
     host->property_trees()->needs_rebuild = true;
     host->GetLayerTree()->RegisterLayer(this);
     if (inputs_.element_id) {
-      host->AddToElementMap(this);
+      host->GetLayerTree()->AddToElementMap(this);
       host->animation_host()->RegisterElement(inputs_.element_id,
                                               ElementListType::ACTIVE);
     }
@@ -1848,7 +1848,7 @@ void Layer::SetElementId(ElementId id) {
   if (inputs_.element_id && layer_tree_host()) {
     layer_tree_host()->animation_host()->UnregisterElement(
         inputs_.element_id, ElementListType::ACTIVE);
-    layer_tree_host()->RemoveFromElementMap(this);
+    layer_tree_->RemoveFromElementMap(this);
   }
 
   inputs_.element_id = id;
@@ -1856,7 +1856,7 @@ void Layer::SetElementId(ElementId id) {
   if (inputs_.element_id && layer_tree_host()) {
     layer_tree_host()->animation_host()->RegisterElement(
         inputs_.element_id, ElementListType::ACTIVE);
-    layer_tree_host()->AddToElementMap(this);
+    layer_tree_->AddToElementMap(this);
   }
 
   SetNeedsCommit();