The client has a setRingtone function that lets you set a single file path or an array of paths, say of mp3 and ogg file formats. It got dropped off from the docs. You can set the your ringtone after you create the client. We will make sure the docs get exported in the next builds.
/**
* Set the sound to be played as the ringtone for calls. The parameter takes an
* array of paths, so that you can pass in different file formats like
* ogg and mp3 for cross browser support.
* @param {!string|!Array.<!string>} audioFilePath path to audio file(s).
*/
setRingtone(<audioPath(s)>)