Please use standard Android API (SYSTEM_UI_FLAG_IMMERSIVE_STICKY) to hide the bar.
http://developer.android.com/training/system-ui/immersive.html
On top of that, IAdea firmware has more beneficial behaviors
- there is no annoying notification as in (2)
- swiping display won't show system bars as in (4)
Note: This method does not work when there is a <select> element on a HTML5 page loaded inside a web view.