Sync the AnimationEvent and TransitionEvent interfaces with the specs

Source/core/events/AnimationEventInit.idl

Index: Source/core/events/AnimationEventInit.idl
diff --git a/Source/core/events/AnimationEventInit.idl b/Source/core/events/AnimationEventInit.idl
index 9a1587b6c503b04c0abebd3c28398eb7e3707ea1..ae6c9b9c9759f6c933d89c9c630258c1d6fe559e 100644
--- a/Source/core/events/AnimationEventInit.idl
+++ b/Source/core/events/AnimationEventInit.idl
@@ -2,9 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Non-standard.
+// http://dev.w3.org/csswg/css-animations/#interface-animationevent
 
 dictionary AnimationEventInit : EventInit {
-    DOMString animationName;
-    double elapsedTime;
+    DOMString animationName = "";
+    // TODO(philipj): elapsedTime should be float.
+    double elapsedTime = 0.0;
+    // TODO(philipj): DOMString pseudoElement = "";
 };