ValidationTool doesn't flag abstract classes as non-default-instantiable Contributed by tbroyer Fixes issue 7414 Review at: https://gwt-code-reviews.appspot.com/1729805/ git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@11051 8db76d5a-ed1c-0410-87a9-c151d255dfc7