Cherry pick r9386, rollback Change Activity to an abstract class

Original review at http://gwt-code-reviews.appspot.com/1200801
Issue 5730


git-svn-id: https://google-web-toolkit.googlecode.com/svn/releases/2.1@9391 8db76d5a-ed1c-0410-87a9-c151d255dfc7
10 files changed