record() {
    this.isRecording = true;
    var media = navigator.mediaDevices.getUserMedia({audio: true})

    media.then(this.startUserMedia.bind(this)).catch(this.onUserMediaError.bind(this));    
    return media;
  }
Request browser microphone access and waits for it resolution.
If the user grant access, Microm will start recording the audio.

@return {Promise}