Add 'colno' attribute to ErrorEvent interface

Add 'colno' attribute to ErrorEvent interface to match the latest
specification:
http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#errorevent

The 'colno' attribute is already supported by IE10.

BUG=264197

Review URL: https://chromiumcodereview.appspot.com/20679002

git-svn-id: svn://svn.chromium.org/blink/trunk@155148 bbb929c8-8fbe-4397-9dbb-9b2b20218538