compositor: Add rAF-like functionality for the UI.

ui/compositor/compositor_animation_observer.h

Index: ui/compositor/compositor_animation_observer.h
diff --git a/ui/compositor/compositor_animation_observer.h b/ui/compositor/compositor_animation_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..facfe5a04824efd37a57bb3d6595a6cf7b3e560c
--- /dev/null
+++ b/ui/compositor/compositor_animation_observer.h
@@ -0,0 +1,22 @@
+// Copyright 2014 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_COMPOSITOR_COMPOSITOR_ANIMATION_OBSERVER_H_
+#define UI_COMPOSITOR_COMPOSITOR_ANIMATION_OBSERVER_H_
+
+#include "base/time/time.h"
+#include "ui/compositor/compositor_export.h"
+
+namespace ui {
+
+class COMPOSITOR_EXPORT CompositorAnimationObserver {
+ public:
+  virtual ~CompositorAnimationObserver() {}
+
+  virtual void OnAnimationStep(base::TimeTicks timestamp) = 0;
+};
+
+}  // namespace ui
+
+#endif  // UI_COMPOSITOR_COMPOSITOR_ANIMATION_OBSERVER_H_