Added a views::test::TestInkDropAnimationObserverHelper

ui/views/animation/animation_observer.h

Index: ui/views/animation/animation_observer.h
diff --git a/ui/views/animation/animation_observer.h b/ui/views/animation/animation_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..f9ec839e7b7a9c02b461a0b06088e4e0a0c203f3
--- /dev/null
+++ b/ui/views/animation/animation_observer.h
@@ -0,0 +1,65 @@
+// Copyright 2016 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_ANIMATION_OBSERVER_H_
+#define UI_VIEWS_ANIMATION_ANIMATION_OBSERVER_H_
+
+#include <string>
+
+#include "base/logging.h"
+#include "base/macros.h"
+#include "ui/views/views_export.h"
+
+namespace views {
+
+// Templated observer class that can be used to observe animations.
+template <typename ContextType>
+class VIEWS_EXPORT AnimationObserver {
+ public:
+  // Enumeration of the different reasons why an animation has finished.
+  enum AnimationEndedReason {
+    // The animation was completed successfully.
+    SUCCESS,
+    // The animation was stopped prematurely before reaching its final state.
+    PRE_EMPTED
+  };
+
+  // Notifies the observer that an animation with the given |context| has
+  // started.
+  virtual void AnimationStarted(ContextType context) = 0;
+
+  // Notifies the observer that an animation with the given |context| 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.
+  virtual void AnimationEnded(ContextType context,
+                              AnimationEndedReason reason) = 0;
+
+ protected:
+  AnimationObserver() {}
+  virtual ~AnimationObserver() {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(AnimationObserver);
+};
+
+// Returns a human readable string for |reason|.  Useful for logging.
+template <typename ContextType>

[sky, 2016/04/20 19:38:47]

Seems like the only reason you need the template parameter here is because the
enum is inside the class. If you move the enum outside the class you won't need
the template param.

[bruthig, 2016/04/20 21:20:08]

Done.

+std::string ToString(
+    typename AnimationObserver<ContextType>::AnimationEndedReason reason) {
+  switch (reason) {
+    case AnimationObserver<ContextType>::SUCCESS:
+      return std::string("SUCCESS");

[sky, 2016/04/20 19:38:47]

nit: no std::string(), just "SUCCESS".

[bruthig, 2016/04/20 21:20:08]

Done.

+    case AnimationObserver<ContextType>::PRE_EMPTED:
+      return std::string("PRE_EMPTED");
+  }
+  NOTREACHED()
+      << "Should never be reached but is necessary for some compilers.";
+  return std::string();
+}
+
+}  // namespace views
+
+#endif  // UI_VIEWS_ANIMATION_ANIMATION_OBSERVER_H_