[Android] Implement the feature of enabling immersive mode for full scre...

...en.

Since Android 4.4 (API Level 19) introduces the immersive related mode
for full screen, in Crosswalk, we need to support this feature accordingly.
This PR is resolving this issue by implementing the specific methods
corresponding to the scenarios that full screen mode is turned on and off.

BUG=https://crosswalk-project.org/jira/browse/XWALK-979