KeyFrameEffect and KeyFrameEffectReadOnly are still built unified as
buddies because they have some complex interdependency that couldn't
easily be resolved without linking failures.
* Add a node property to access the ::before and ::after pseudo-elements
* Look for the frame for ::before and ::after pseudos
* Clean up pseudo-element props
* Simplify nsLayoutUtils callers, and make child iterators notice display: contents pseudos
Tag #1375
Issue #55
part 1 - Add transitioncancel event handler
part 2 - Add ontransitioncancel EventHandler to WebIDL
part 3 - Add member of active time to ComputedTiming