Augment userAgent detection

Add a userAgent detection for Chrome.
Rework detection using [RegExp#test](https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/RegExp/test) to make the checks more efficient.
Make the `vjs.IS_ANDROID` just check for android so that it can be used in conjunction with the firefox and chrome checks.
Fix `vjs.IS_FIREFOX` being a function that is used as a property by making it be a property like the other predicates.