View source for QA/App Sharing

App Sharing is a feature currently targeted for Firefox 34 that uses WebRTC for screensharing all windows of an app. 

To test app sharing:
* start multiple applications
* start Firefox Nightly 34
* set media.getusermedia.screensharing.enabled = true 
* set media.getusermedia.screensharing.allowed_domains = queze.net
* open http://queze.net/goinfre/ff_gum_test.html
* start Application
* click on the "Application to share:" drop-down to get the list of
applications

Meta bugs:
<bugzilla>
    {
        "id": ["923225","1053215","1040061","1036653"]
 
    }
</bugzilla>