[wrt][xwalk-2412] Update case description

Impacted TCs num(approved): New 0, Update 1, Delete 0
Unit test Platform: Android
Android test result summary: Pass 1, Fail 0, Block 0
Merge pull request #808 from wanghongjuan/wanghongjuan/wrt/xwalk-2412

[wrt][xwalk-2412] Update case description