Support latest ChromeDriver commands

[ventuno]

ChromeDriver version 2.30 [1] will support 2 new endpoints to send custom commands to the DevTools debugger server:

• /chromium/send_command;
• /chromium/send_command_and_get_result.

In this PR, I add the support for these new commands to the webdriver-js-extender.

[1] https://chromium.googlesource.com/chromium/src/+/711de0efbb675bd2a4a28ec47c9194d8e498e600

[googlebot]

We found a Contributor License Agreement for you (the sender of this pull request), but were unable to find agreements for the commit author(s). If you authored these, maybe you used a different email address in the git commits than was used to sign the CLA (login here to double check)? If these were authored by someone else, then they will need to sign a CLA as well, and confirm that they're okay with these being contributed to Google.

[ventuno]

Dear @sjelin, any chance this could be reviewed soon? I'm not sure what the @googlebot is complaining about, I already signed the CLA and it's linked to my github account :-).

[ventuno]

Dear @sjelin, any chance this could be reviewed soon? Chromedriver version 2.30 was released already :-).

[ventuno]

@qiyigg this has been open for the longest time. Any chance it could be reviewed and merged? I tried pinging @sjelin, but he doesn't seem to be active anymore on this repo.

I'm not sure why the CLA checks are failing, but I already signed it on Mar 14, 2017.

[ventuno]

Closing in favor of #21.