Enhanced the InkDropRippleImpl to create/destroy InkDropAnimations as needed.

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
new file mode 100644
index 0000000000000000000000000000000000000000..08090f39dcacf07d45d7ae0eb66582d88dd116a9
--- /dev/null
+++ b/ui/views/animation/ink_drop_animation_observer.h
@@ -0,0 +1,57 @@
+// 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 <string>
+
+#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 prematurely before reaching its final state.
+    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 its final frame however if |reason|
+  // is |PRE_EMPTED| then the animation was stopped before its final frame. In
+  // the event that an animation is in progress for ink drop state 's1' and an
+  // animation to a new state 's2' is triggered, then
+  // InkDropAnimationEnded(s1, PRE_EMPTED) will be called before
+  // InkDropAnimationStarted(s2).
+  virtual void InkDropAnimationEnded(InkDropState ink_drop_state,
+                                     InkDropAnimationEndedReason reason) = 0;
+
+ protected:
+  InkDropAnimationObserver() {}
+  virtual ~InkDropAnimationObserver() {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(InkDropAnimationObserver);
+};
+
+// Returns a human readable string for |reason|.  Useful for logging.
+std::string ToString(
+    InkDropAnimationObserver::InkDropAnimationEndedReason reason);
+
+}  // namespace views
+
+#endif  // UI_VIEWS_ANIMATION_INK_DROP_ANIMATION_OBSERVER_H_