[webapi][XWALK-1951] Update case description for csp

Impacted TCs num: New 0, Update 1, Delete 0
Unit test Platform: [Tizen IVI]
Test result summary: Pass 1, Fail 0, Blocked 0
Merge pull request #371 from JianfengXu/xujf/webapi/csp

[webapi][XWALK-1951] Update case description for csp