[webapi] Add 52 TCs for native file api
Impacted Suites: webapi-nativefilesystem-xwalk-tests
Impacted TCs num: New 52, update 0, deleted 0
Unit test Platform: IVI
IVI test result summary: Pass 0, Fail 52, Blocked 0

Fail Reason:
All cases are designed, because the Native File API is not ready. Jira link: https://crosswalk-project.org/jira/browse/XWALK-672
Merge pull request #190 from yunxliu/yunxliu/webapi/webapi-filesystem-xwalk-tests

[webapi] Add 52 TCs for native file api