We need a way to manipulate the B2G profile before we run Marionette tests. In the short term this will help us solve the sleep-after-60s problem (bug 739476), but longer-term we will need this functionality for running mochitest and reftest on B2G as well. I imagine the implementation will use adb to locate the profile, and either modify it, or create a new profile using the existing one as a template, and then reboot the device so that the changes get picked up. Possible modifications include adding/modifying prefs, and adding extensions, although to what extent extensions will work in B2G is unclear. We will want the ability to restore the device to the original profile as well, which might just mean modifying profiles.ini to set the original default profile as the present default. There are a few different parts to implementing this, so I may add individual bugs for those parts and leave this as a tracking bug.