Enhanced the InkDropRippleImpl to create/destroy InkDropAnimations as needed.

ui/views/animation/ink_drop_animation_observer.h

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_VIEWS_ANIMATION_INK_DROP_ANIMATION_OBSERVER_H_
+#define UI_VIEWS_ANIMATION_INK_DROP_ANIMATION_OBSERVER_H_
+
+#include <iosfwd>
+
+#include "base/macros.h"
+#include "ui/views/animation/ink_drop_state.h"
+#include "ui/views/views_export.h"
+
+namespace views {
+
+// Pure-virtual base class of an observer that can be attached to
+// InkDropAnimations.
+class VIEWS_EXPORT InkDropAnimationObserver {
+ public:
+  // Enumeration of the different reasons why an InkDropAnimation has finished.
+  enum InkDropAnimationEndedReason {
+    // The animation was completed successfully.
+    SUCCESS,
+    // The animation was stopped pre-maturely before reaching it's final state.

[varkha, 2015/10/06 20:58:38]

nit: s/pre-maturely/prematurely ; s/it's/its

[bruthig, 2015/10/08 21:42:55]

Done.

+    PRE_EMPTED
+  };
+
+  // Notifies the observer that an animation for |ink_drop_state| has started.
+  virtual void InkDropAnimationStarted(InkDropState ink_drop_state) = 0;
+
+  // Notifies the observer that an animation for |ink_drop_state| has finished
+  // and the reason for completion is given by |reason|. If |reason| is SUCCESS
+  // then the animation has progressed to it's final frame however if |reason|

[varkha, 2015/10/06 20:58:38]

nit: here and below - s/it's/its.

[bruthig, 2015/10/08 21:42:55]

Done.

+  // is |PRE_EMPTED| then the animation was stopped before it's final frame.

[sadrul, 2015/10/08 01:06:01]

Is it possible to start the animation for one state while another animation was
in progress? If that is the case, then I assume Ended() is triggered with
PRE_EMPTED before Started() is called again for the new state? Can you clarify
that in this comment?

[bruthig, 2015/10/08 21:42:55]

Done.

+  virtual void InkDropAnimationEnded(InkDropState ink_drop_state,
+                                     InkDropAnimationEndedReason reason) = 0;
+
+ protected:
+  InkDropAnimationObserver() {}
+  virtual ~InkDropAnimationObserver() {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(InkDropAnimationObserver);
+};
+
+VIEWS_EXPORT std::ostream& operator<<(

[sadrul, 2015/10/08 01:06:01]

Is this actually useful/necessary?

[bruthig, 2015/10/08 21:42:55]

Replaced with a ToString().

+    std::ostream& out,
+    InkDropAnimationObserver::InkDropAnimationEndedReason reason);
+
+}  // namespace views
+
+#endif  // UI_VIEWS_ANIMATION_INK_DROP_ANIMATION_OBSERVER_H_