Enhanced the InkDropRippleImpl to create/destroy InkDropAnimations as needed.

ui/views/animation/ink_drop_animation_observer.cc

+// 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.
+
+#include "ui/views/animation/ink_drop_animation_observer.h"
+
+#include <iostream>
+#include <string>
+
+#include "base/logging.h"
+
+namespace views {
+
+std::string ToString(
+    InkDropAnimationObserver::InkDropAnimationEndedReason reason) {
+  switch (reason) {
+    case InkDropAnimationObserver::SUCCESS:
+      return std::string("SUCCESS");
+    case InkDropAnimationObserver::PRE_EMPTED:
+      return std::string("PRE_EMPTED");
+  }
+  NOTREACHED()
+      << "Should never be reached but is necessary for some compilers.";
+  return std::string();
+}
+
+}  // namespace views