Document the Web Animation interfaces with spec links and TODOs

Source/core/animation/AnimationNode.idl

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
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  * modification, are permitted provided that the following conditions are
  * met:
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  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 10 matching lines @@
  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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+// http://www.w3.org/TR/web-animations/#the-animationnode-interface
+
+// TODO(dstockwell): This interface has been renamed to AnimationEffectReadonly
+// in the latest spec:
+// https://w3c.github.io/web-animations/#the-animationeffectreadonly-interface
+
 [
     RuntimeEnabled=WebAnimationsAPI,
     WillBeGarbageCollected,
 ] interface AnimationNode {
     readonly attribute Timing timing;
     readonly attribute ComputedTimingProperties computedTiming;
 };