Refactor MutatorHostClient from LayerTreeHost to LayerTree.

cc/trees/layer_tree_host_common_unittest.cc

Index: cc/trees/layer_tree_host_common_unittest.cc
diff --git a/cc/trees/layer_tree_host_common_unittest.cc b/cc/trees/layer_tree_host_common_unittest.cc
index 09e196eeee3e04820a79eeea76bde37fafe61ef4..d54ce093acc15cf4f407c0cb1920269415c92ca3 100644
--- a/cc/trees/layer_tree_host_common_unittest.cc
+++ b/cc/trees/layer_tree_host_common_unittest.cc
@@ -4871,12 +4871,13 @@ TEST_F(LayerTreeHostCommonTest, LayerSearch) {
   host()->SetRootLayer(root);
 
   int nonexistent_id = -1;
-  EXPECT_EQ(root.get(), host()->LayerById(root->id()));
-  EXPECT_EQ(child.get(), host()->LayerById(child->id()));
-  EXPECT_EQ(grand_child.get(), host()->LayerById(grand_child->id()));
-  EXPECT_EQ(mask_layer.get(), host()->LayerById(mask_layer->id()));
-  EXPECT_EQ(replica_layer.get(), host()->LayerById(replica_layer->id()));
-  EXPECT_FALSE(host()->LayerById(nonexistent_id));
+  LayerTree* layer_tree = host()->GetLayerTree();
+  EXPECT_EQ(root.get(), layer_tree->LayerById(root->id()));
+  EXPECT_EQ(child.get(), layer_tree->LayerById(child->id()));
+  EXPECT_EQ(grand_child.get(), layer_tree->LayerById(grand_child->id()));
+  EXPECT_EQ(mask_layer.get(), layer_tree->LayerById(mask_layer->id()));
+  EXPECT_EQ(replica_layer.get(), layer_tree->LayerById(replica_layer->id()));
+  EXPECT_FALSE(layer_tree->LayerById(nonexistent_id));
 }
 
 TEST_F(LayerTreeHostCommonTest, TransparentChildRenderSurfaceCreation) {