Added a nested class to gfx::Animation

ui/gfx/animation/animation_test_api.h

Index: ui/gfx/animation/animation_test_api.h
diff --git a/ui/gfx/animation/animation_test_api.h b/ui/gfx/animation/animation_test_api.h
new file mode 100644
index 0000000000000000000000000000000000000000..07aa01d5c7ef3dbf79a72860c9562f6b02d580d7
--- /dev/null
+++ b/ui/gfx/animation/animation_test_api.h
@@ -0,0 +1,32 @@
+// Copyright (c) 2017 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_GFX_ANIMATION_ANIMATION_TEST_API_H_
+#define UI_GFX_ANIMATION_ANIMATION_TEST_API_H_
+
+#include "ui/gfx/animation/animation.h"
+
+namespace gfx {
+
+// Class to provide access to Animation internals for testing.
+class ANIMATION_EXPORT Animation::AnimationTestApi {
+ public:
+  explicit AnimationTestApi(Animation* animation);
+  ~AnimationTestApi();
+
+  // Sets the start of the animation.
+  void SetStartTime(base::TimeTicks ticks);
+
+  // Manually steps the animation forward
+  void Step(base::TimeTicks ticks);
+
+ private:
+  Animation* animation_;
+
+  DISALLOW_COPY_AND_ASSIGN(AnimationTestApi);
+};
+
+}  // namespace gfx
+
+#endif  // UI_GFX_ANIMATION_ANIMATION_TEST_API_H_