Attempt to fix flakiness in testGetClientSize by bumping up the timeout.
(I didn't track down the root cause.)

Review at http://gwt-code-reviews.appspot.com/1814803

Review by: mdempsky@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@11233 8db76d5a-ed1c-0410-87a9-c151d255dfc7