createChannel = (label) => { // eslint-disable-line
      const fns = [];
      return {
        addListener: (...args) => {
          // console.info(extensionId, label, 'addL', args);
          fns.push(args[0]);
        },
        removeListener: () => {
          // console.info(extensionId, label, 'removeL', args);
        },
        call: (...args) => fns.forEach(fn => fn(...args)),
      };
    }
This is effectively voodoo, basically we fake being the official Google Play Music
Mini Player and receive a whole bunch of handy events.  Would love to rewrite gmusic.js
to use this but really don't have the time.