Sync the AnimationEvent and TransitionEvent interfaces with the specs

Source/core/events/AnimationEvent.idl

Index: Source/core/events/AnimationEvent.idl
diff --git a/Source/core/events/AnimationEvent.idl b/Source/core/events/AnimationEvent.idl
index fdf46af5d2c507dcad13f452101f5acfd6861fc5..8b0b7945a5b353c7c0dbbb84410f3decd3a9feb2 100644
--- a/Source/core/events/AnimationEvent.idl
+++ b/Source/core/events/AnimationEvent.idl
@@ -23,10 +23,13 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+// http://dev.w3.org/csswg/css-animations/#interface-animationevent
+
 [
     Constructor(DOMString type, optional AnimationEventInit eventInitDict),
 ] interface AnimationEvent : Event {
     readonly attribute DOMString animationName;
+    // TODO(philipj): elapsedTime should be float.
     readonly attribute double elapsedTime;
+    // TODO(philipj): readonly attribute DOMString pseudoElement;
 };
-