[webapi] Update 2 tests for WebRTC to reflect Crosswalk spec

Impacted Suites: webapi-webrtc-w3c-tests
Impacted Tcs num: New 0, Update 2, Delete 0
Unit test platform: Tizen ivi
Tizen ivi test result summary: Pass 1, Fail 1, Blocked 0

Fail Reason:
Feature issue, the first argument's type of getStats function is error.