IDL compiler: addEventListener, removeEventListener methods

Last methods CL!
(Still lots of cleanup, then on to interfaces.)

Also:
Renaming 'special' to 'exceptional' in comments, as 'special' has technical
meaning in Web IDL (special operations, special keywords, etc.).

BUG=239771

Review URL: https://codereview.chromium.org/70963003

git-svn-id: svn://svn.chromium.org/blink/trunk@161913 bbb929c8-8fbe-4397-9dbb-9b2b20218538