[misc] Integrate latest testharness.js framework into system tests

- http://github.com/w3c/testharness.js/
- commit b8c9ce09cd031e8a732bbfc0a8c81f674ffa8a49
[misc] Integrate W3C navigator.language test case

https://github.com/w3c/web-platform-tests/blob/master/workers/interfaces/WorkerUtils/navigator/language.html

BUG=https://crosswalk-project.org/jira/browse/XWALK-2242
[misc] Remove '<!-- -->' from the start of .html file as workaround

BUG=https://crosswalk-project.org/jira/browse/XWALK-2293
This shall be a Crosswalk implementation issue, maybe Chromium's.
Merge pull request #682 from zqzhang/zqzhang/navigator-language-w3c

[misc][XWALK-2242] Integrate W3C navigator.language test case