Follow up to r9887, to actually sink ended and progress media events in DOMImplStandard

Review at http://gwt-code-reviews.appspot.com/1385804

Review by: pdr@google.com


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9918 8db76d5a-ed1c-0410-87a9-c151d255dfc7