Fix issue with NPAPI plugin being removed from auth list after some visit to chrome://plugins. The issue is actually not specifically related to the visit to chrome://plugins. After a certain amount of time (usually a few mns) an plugin update service is triggered that updates the plugin list (it occurs something like once every day), and pulls data from the server side plugin list https://www.gstatic.com/chrome/config/plugins_linux.json and overrides our already altered list (therefore removes our additional reference to webapps plugin). Fixes: https://bugs.launchpad.net/bugs/1108116.
Approved by Alexandre Abreu, PS Jenkins bot.