https://bugs.webkit.org/show_bug.cgi?id=121751

Reviewed by Andreas Kling.

Convert the Event and EventTarget interface identifiers from AtomicStrings to enums. They
are not extensible and not exposed as Strings anywhere.

* Files elided *



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@156241 268f45cc-cd09-0410-ab3c-d52691b4dbfc