Chrome Extension friendly protocol check

[brentchow]

Improvements:

• Modified to check for the protocol chrome-extension: and use https:// if found. This should make this library friendly for anyone building a Chrome Extension

[coveralls]

Coverage remained the same at 96.269% when pulling bd0a9ea on brentchow:chrome-extension-protocol into e10fb3b on aleross:master.

[brentchow]

https is required as per https://developer.chrome.com/extensions/contentSecurityPolicy#relaxing-remote-script