[webapi][XWALK-3189] Integrate 2 audio tests from W3C

Impacted TCs num(approved): New 0, Update 2, Delete 0
Unit test Platform: [Tizen-IVI]
Unit test result summary: Pass 2, Fail 0, Blocked 0
Merge pull request #1511 from JianfengXu/audio/3189

[webapi][XWALK-3189] Integrate 2 audio tests from W3C