cc: Clean up root_layer code in LTI

cc/test/layer_test_common.h

Index: cc/test/layer_test_common.h
diff --git a/cc/test/layer_test_common.h b/cc/test/layer_test_common.h
index 094be5d859cbb3bc03d75226ea62d554a4f73a75..f99b85b8c956034dd66c88d24cdec8b267572386 100644
--- a/cc/test/layer_test_common.h
+++ b/cc/test/layer_test_common.h
@@ -61,7 +61,7 @@ class LayerTestCommon {
       std::unique_ptr<T> layer =
           T::Create(host_->host_impl()->active_tree(), layer_impl_id_++);
       T* ptr = layer.get();
-      root_layer()->test_properties()->AddChild(std::move(layer));
+      root_layer_for_testing()->test_properties()->AddChild(std::move(layer));
       return ptr;
     }
 
@@ -88,7 +88,7 @@ class LayerTestCommon {
       std::unique_ptr<T> layer =
           T::Create(host_->host_impl()->active_tree(), layer_impl_id_++, a);
       T* ptr = layer.get();
-      root_layer()->test_properties()->AddChild(std::move(layer));
+      root_layer_for_testing()->test_properties()->AddChild(std::move(layer));
       return ptr;
     }
 
@@ -97,7 +97,7 @@ class LayerTestCommon {
       std::unique_ptr<T> layer =
           T::Create(host_->host_impl()->active_tree(), layer_impl_id_++, a, b);
       T* ptr = layer.get();
-      root_layer()->test_properties()->AddChild(std::move(layer));
+      root_layer_for_testing()->test_properties()->AddChild(std::move(layer));
       return ptr;
     }
 
@@ -106,7 +106,7 @@ class LayerTestCommon {
       std::unique_ptr<T> layer = T::Create(host_->host_impl()->active_tree(),
                                            layer_impl_id_++, a, b, c, d);
       T* ptr = layer.get();
-      root_layer()->test_properties()->AddChild(std::move(layer));
+      root_layer_for_testing()->test_properties()->AddChild(std::move(layer));
       return ptr;
     }
 
@@ -124,7 +124,7 @@ class LayerTestCommon {
       std::unique_ptr<T> layer = T::Create(host_->host_impl()->active_tree(),
                                            layer_impl_id_++, a, b, c, d, e);
       T* ptr = layer.get();
-      root_layer()->test_properties()->AddChild(std::move(layer));
+      root_layer_for_testing()->test_properties()->AddChild(std::move(layer));
       return ptr;
     }
 
@@ -145,8 +145,8 @@ class LayerTestCommon {
     ResourceProvider* resource_provider() const {
       return host_->host_impl()->resource_provider();
     }
-    LayerImpl* root_layer() const {
-      return host_impl()->active_tree()->root_layer();
+    LayerImpl* root_layer_for_testing() const {
+      return host_impl()->active_tree()->root_layer_for_testing();
     }
     FakeLayerTreeHost* host() { return host_.get(); }
     FakeLayerTreeHostImpl* host_impl() const { return host_->host_impl(); }