Fix problem where hidden scrollbars prevent clicks through to the scrollable content area on Chrome(webkit?) browsers on Windows.

https://code.google.com/p/google-web-toolkit/issues/detail?id=7576

This is not a fix for the same/similar issue on Mac OS for Chrome and Safari.

Fix suggested by Steven Arth:
https://code.google.com/p/google-web-toolkit/issues/detail?id=7576#c34

Review at http://gwt-code-reviews.appspot.com/1886803


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@11480 8db76d5a-ed1c-0410-87a9-c151d255dfc7