Bug 873931 - Statusbar does not show when fullscreen is canceled.

https://bugzilla.mozilla.org/show_bug.cgi?id=873931

1. Title : [System][Statusbar] Statusbar does not show when fullscreen is canceled.
2. Precondition : Run an app that has an option to turn fullscreen mode on/off.
3. Tester's Action : Turn fullscreen mode on and off.
4. Detailed Symptom (ENG.) : Observe the statusbar is not displayed. Instead, you can see through the homescrean background.
5. Expected : The statusbar should be displayed.
6.Reproducibility: Y
           1)Frequency Rate : 100%
7.Gaia Revision: a503d9a1d0a588f3689243c1ddc0f016ede51b9d
8.Personal email id:  hanj.kim25@gmail.com

This is a regression from Bug 834765.