Add a permissions model to the Chrome NPAPI plugin.

Permissions are stored in localstorage of the background page.
They can be changed by navigating to the extension's options page.
A page action indicates if the plugin permissions are good or bad for the current host.

Review at http://gwt-code-reviews.appspot.com/1084801


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@9283 8db76d5a-ed1c-0410-87a9-c151d255dfc7