onEvent_(eventType, region, seeking) {
    const event = new shaka.util.FakeEvent(eventType, new Map([
      ['region', region],
      ['seeking', seeking],
    ]));
    this.dispatchEvent(event);
  }
Dispatch events of the given type.  All event types in this class have the
same parameters: region and seeking.

@param {string} eventType
@param {T} region
@param {boolean} seeking
@private