Refactor MutatorHostClient from LayerTreeHost to LayerTree.

cc/test/layer_test_common.cc

Index: cc/test/layer_test_common.cc
diff --git a/cc/test/layer_test_common.cc b/cc/test/layer_test_common.cc
index bf7a0aa4df887218ac745c72041d4ed196e53355..4e6298d5a65e15158016c5ab776d4627de243fdc 100644
--- a/cc/test/layer_test_common.cc
+++ b/cc/test/layer_test_common.cc
@@ -132,16 +132,16 @@ LayerTestCommon::LayerImplTest::LayerImplTest(const LayerTreeSettings& settings)
 
   const int timeline_id = AnimationIdProvider::NextTimelineId();
   timeline_ = AnimationTimeline::Create(timeline_id);
-  host_->animation_host()->AddAnimationTimeline(timeline_);
+  host_->GetLayerTree()->animation_host()->AddAnimationTimeline(timeline_);
   // Create impl-side instance.
-  host_->animation_host()->PushPropertiesTo(
+  host_->GetLayerTree()->animation_host()->PushPropertiesTo(
       host_->host_impl()->animation_host());
   timeline_impl_ =
       host_->host_impl()->animation_host()->GetTimelineById(timeline_id);
 }
 
 LayerTestCommon::LayerImplTest::~LayerImplTest() {
-  host_->animation_host()->RemoveAnimationTimeline(timeline_);
+  host_->GetLayerTree()->animation_host()->RemoveAnimationTimeline(timeline_);
   timeline_ = nullptr;
   host_->host_impl()->ReleaseOutputSurface();
 }