Public:  First take at GWT validation that actually validates on the client side.

Review at http://gwt-code-reviews.appspot.com/863801

Review by: robertvawter@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@8952 8db76d5a-ed1c-0410-87a9-c151d255dfc7