[Android] Fix the issue about control bar disappeared in fullscreen of
landscape.

This patch is to fix the issue that control bar disappeared in
fullscreen when screen's orientation changed to landscape.
Add the XWalkView to activity's Decor view.

BUG=XWALK-3048
Merge pull request #2747 from wuhengzhi/xwalk_3048_video_control_disappear

[Android] Fix the issue about control bar disappeared in fullscreen of