Re-roll r870801.

*** Original Change Description ***

Reduce DevMode memory footprint by using a WeakInterner for potentially duplicated strings

Review at http://gwt-code-reviews.appspot.com/870801


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@8850 8db76d5a-ed1c-0410-87a9-c151d255dfc7