[usecase-system][XWALK-1473] Add a TC for WebRTC

- Add a TC for WebRTC
- Failure analysis: The first channel onDataChannel can not be fired and the data channel name cannot be with space inside

Impacted tests(approved): new 0, update 1, delete 0
Unit test platform: [Android]
Unit test result summary: pass 0, fail 1, block 0
Merge pull request #730 from yunxliu/yunxliu/misc/webrtc_google

[usecase-system][XWALK-1473] Add a TC for WebRTC