detect chrome version: specify channel

[kylemorelock]

Running into an issue when detecting chrome version. If a user has multiple channels installed across users, the option for detecting chrome version always will return the largest version number. This presents a problem for utils like https://github.com/giggio/node-chromedriver which download chromedriver. see giggio/node-chromedriver#364

Could we provide an option to specify which channel we want to get the chrome version for? This way, a system could have multiple channels of chrome installed and user could specify which channel they would like to use for getting the version

[benjamingr]

@MoLow @omril1