Animations: Introduce compositor AnimationPlayer and AnimationTimeline.

public/platform/WebCompositorAnimationTimeline.h

+// 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 WebCompositorAnimationTimeline_h
+#define WebCompositorAnimationTimeline_h
+
+namespace blink {
+
+class WebCompositorAnimationPlayerClient;
+
+// A compositor representation for timeline.
+class WebCompositorAnimationTimeline {
+public:
+    virtual ~WebCompositorAnimationTimeline() { }
+
+    virtual void playerAttached(const WebCompositorAnimationPlayerClient&) { }
+    virtual void playerDestroyed(const WebCompositorAnimationPlayerClient&) { }
+};
+
+} // namespace blink
+
+#endif // WebCompositorAnimationTimeline_h