Adds overflow-x and overflow-y to Style since they have at least partial support on all browsers.
Review at: http://gwt-code-reviews.appspot.com/1100801
Review by: jgw


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9234 8db76d5a-ed1c-0410-87a9-c151d255dfc7