cc: Make LayerTreeHost a protected Layer member.

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 834094dcbdf5b722bf4a67b27126c6ec9c999f58..c8fe6ce451e45fea441629b178a4684c6446df47 100644
--- a/cc/trees/layer_tree_host_common_unittest.cc
+++ b/cc/trees/layer_tree_host_common_unittest.cc
@@ -9543,7 +9543,7 @@ TEST_F(LayerTreeHostCommonTest, OpacityAnimationsTrackingTest) {
   EXPECT_TRUE(node->has_potential_opacity_animation);
 
   animation_ptr->set_time_offset(base::TimeDelta::FromMilliseconds(0));
-  root->layer_tree_host()->AnimateLayers(
+  root->GetLayerTreeHostForTesting()->AnimateLayers(
       base::TimeTicks::FromInternalValue(std::numeric_limits<int64_t>::max()));
   node = tree.Node(animated->effect_tree_index());
   EXPECT_TRUE(node->is_currently_animating_opacity);
@@ -9600,7 +9600,7 @@ TEST_F(LayerTreeHostCommonTest, TransformAnimationsTrackingTest) {
   EXPECT_TRUE(node->has_potential_animation);
 
   animation_ptr->set_time_offset(base::TimeDelta::FromMilliseconds(0));
-  root->layer_tree_host()->AnimateLayers(
+  root->GetLayerTreeHostForTesting()->AnimateLayers(
       base::TimeTicks::FromInternalValue(std::numeric_limits<int64_t>::max()));
   node = tree.Node(animated->transform_tree_index());
   EXPECT_TRUE(node->is_currently_animating);