[usecase-webapi] Reduce the display area to fit the mobile screen for gamepad

- Fail Reason:[XWALK-2549]

Impacted TCs num(approved): New 0, Update 1, Delete 0
Unit test Platform: [Android]
Unit test result summary: Pass 0, Fail 1, Blocked 0
Merge pull request #908 from JianfengXu/xujf/gamepad/optimize

[usecase-webapi] Reduce the display area to fit the mobile screen for gamepad