cc: Move LayerImpl::AddChild and RemoveChild to LayerImplTestProperties

cc/layers/layer_impl.h

Index: cc/layers/layer_impl.h
diff --git a/cc/layers/layer_impl.h b/cc/layers/layer_impl.h
index 2f63421d78b24dc12432904ca416743322545f8d..1df7a800e3798cc059b80e903e46f5103ba147c8 100644
--- a/cc/layers/layer_impl.h
+++ b/cc/layers/layer_impl.h
@@ -101,10 +101,6 @@ class CC_EXPORT LayerImpl {
   void OnOpacityIsPotentiallyAnimatingChanged(bool has_potential_animation);
   bool IsActive() const;
 
-  // Tree structure.
-  void AddChild(std::unique_ptr<LayerImpl> child);
-  std::unique_ptr<LayerImpl> RemoveChildForTesting(LayerImpl* child);
-
   void DistributeScroll(ScrollState* scroll_state);
   void ApplyScroll(ScrollState* scroll_state);