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

ui/views/animation/ink_drop_animation_controller_impl.h

Index: ui/views/animation/ink_drop_animation_controller_impl.h
diff --git a/ui/views/animation/ink_drop_animation_controller_impl.h b/ui/views/animation/ink_drop_animation_controller_impl.h
index e0759750e9fdbf5f727c885366714967298fd32a..31971811d4cc904fd9c2d6dcd8abbe4ded4480a4 100644
--- a/ui/views/animation/ink_drop_animation_controller_impl.h
+++ b/ui/views/animation/ink_drop_animation_controller_impl.h
@@ -12,6 +12,7 @@
 #include "ui/gfx/geometry/size.h"
 #include "ui/views/animation/ink_drop_animation_controller.h"
 #include "ui/views/animation/ink_drop_animation_observer.h"
+#include "ui/views/animation/ink_drop_hover_observer.h"
 #include "ui/views/views_export.h"
 
 namespace base {
@@ -31,7 +32,8 @@ class InkDropAnimationControllerFactoryTest;
 // A functional implementation of an InkDropAnimationController.
 class VIEWS_EXPORT InkDropAnimationControllerImpl
     : public InkDropAnimationController,
-      public InkDropAnimationObserver {
+      public InkDropAnimationObserver,
+      public InkDropHoverObserver {
  public:
   // Constructs an ink drop controller that will attach the ink drop to the
   // given |ink_drop_host|.
@@ -66,6 +68,12 @@ class VIEWS_EXPORT InkDropAnimationControllerImpl
   // Destroys the current |hover_|.
   void DestroyInkDropHover();
 
+  // Conditionally adds the |root_layer_| to the |ink_drop_host_|.
+  void AddRootLayerToHost();

[varkha, 2016/04/28 20:35:00]

MaybeAddRootLayerToHost? Also I think it could be possible to document right
here when that "maybe" is true.

[bruthig, 2016/04/29 11:02:34]

I've opted to use the 'IfNeeded' Suffix.  WDYT?

+
+  // Conditionally removes the |root_layer_| from the |ink_drop_host_|.
+  void RemoveRootLayerFromHost();
+
   // Returns true if the hover animation is in the process of fading in or
   // is visible.
   bool IsHoverFadingInOrVisible() const;
@@ -75,6 +83,11 @@ class VIEWS_EXPORT InkDropAnimationControllerImpl
   void AnimationEnded(InkDropState ink_drop_state,
                       InkDropAnimationEndedReason reason) override;
 
+  // views::InkDropHoverObserver:
+  void AnimationStarted(InkDropHover::AnimationType animation_type) override;
+  void AnimationEnded(InkDropHover::AnimationType animation_type,
+                      InkDropAnimationEndedReason reason) override;
+
   // Enables or disables the hover state based on |is_hovered| and if an
   // animation is triggered it will be scheduled to have the given
   // |animation_duration|. If |explode| is true the hover will expand as it
@@ -102,6 +115,9 @@ class VIEWS_EXPORT InkDropAnimationControllerImpl
   // from the InkDropHost.
   std::unique_ptr<ui::Layer> root_layer_;
 
+  // True when the |root_layer_| has been added to the |ink_drop_host_|.
+  bool root_layer_added_to_host_;
+
   // The current InkDropHover. Lazily created using CreateInkDropHover();

[varkha, 2016/04/28 20:35:00]

Not sure about it myself and definitely not in this CL but maybe InkDropHover
should be InkDropHoverAnimation and InkDropAnimation should be
InkDropHoverRippleAnimation. alternatively consider simpler InkDropHover and
InkDropRipple. Either will bring the names closer to point the similarities.

[bruthig, 2016/04/29 11:02:34]

100% agreed.  I was thinking InkDropRipple and InkDropHover.  I just didn't want
to do this rename while I was still merging stuff back to M51.

   std::unique_ptr<InkDropHover> hover_;