Add MD Ink Drop Layers to InkDropHost only when a ripple/hover is active.

ui/views/animation/ink_drop_animation_observer.h

Index: ui/views/animation/ink_drop_animation_observer.h
diff --git a/ui/views/animation/ink_drop_animation_observer.h b/ui/views/animation/ink_drop_animation_observer.h
index bb306c9274993b1f51e1ae602c90ffb4e51e0d17..831a6be06b3b6065eb4856ef342d3569a6daa905 100644
--- a/ui/views/animation/ink_drop_animation_observer.h
+++ b/ui/views/animation/ink_drop_animation_observer.h
@@ -29,8 +29,8 @@ class VIEWS_EXPORT InkDropAnimationObserver {
                               InkDropAnimationEndedReason reason) = 0;
 
  protected:
-  InkDropAnimationObserver() {}
-  virtual ~InkDropAnimationObserver() {}
+  InkDropAnimationObserver() = default;
+  virtual ~InkDropAnimationObserver() = default;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(InkDropAnimationObserver);