Refactor MutatorHostClient from LayerTreeHost to LayerTree.

cc/test/fake_layer_tree_host.cc

Index: cc/test/fake_layer_tree_host.cc
diff --git a/cc/test/fake_layer_tree_host.cc b/cc/test/fake_layer_tree_host.cc
index 9d3ae6fd2eb717d3f3a5d9733e916074ef4efca9..72dd6f093556b9a52520b2a020943fe9bfa16125 100644
--- a/cc/test/fake_layer_tree_host.cc
+++ b/cc/test/fake_layer_tree_host.cc
@@ -92,7 +92,7 @@ LayerImpl* FakeLayerTreeHost::CommitAndCreateLayerImplTree() {
   active_tree()->SetPropertyTrees(property_trees());
   TreeSynchronizer::PushLayerProperties(root_layer()->GetLayerTree(),
                                         active_tree());
-  animation_host()->PushPropertiesTo(host_impl_.animation_host());
+  layer_tree_->animation_host()->PushPropertiesTo(host_impl_.animation_host());
 
   active_tree()->UpdatePropertyTreeScrollOffset(property_trees());
 
@@ -114,7 +114,7 @@ LayerImpl* FakeLayerTreeHost::CommitAndCreatePendingTree() {
   pending_tree()->SetPropertyTrees(property_trees());
   TreeSynchronizer::PushLayerProperties(root_layer()->GetLayerTree(),
                                         pending_tree());
-  animation_host()->PushPropertiesTo(host_impl_.animation_host());
+  layer_tree_->animation_host()->PushPropertiesTo(host_impl_.animation_host());
 
   pending_tree()->UpdatePropertyTreeScrollOffset(property_trees());
   return pending_tree()->root_layer_for_testing();