DevTools wants to use wake lock to keep screen. But since MozWakeLock is
removed by bug 1369194, there is no way to unlock wake lock from script.
So this issue adds nsIWakeLock to unlock wake lock.
Differential Revision: https://phabricator.services.mozilla.com/D7158
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extra : rebase_source : 4d6069fce27a7d85ce484a1418a8a17de83166f1