testChannelMessage_stringDataSupported() {
    const webChannelTransport = new WebChannelBaseTransport();
    webChannel = webChannelTransport.createWebChannel(channelUrl);

    let eventFired = false;
    const data = 'foo';
    events.listen(webChannel, WebChannel.EventType.MESSAGE, (e) => {
      eventFired = true;
      assertEquals(data, e.data);
    });

    webChannel.open();
    assertFalse(eventFired);

    /** @suppress {strictMissingProperties} Accessing private property. */
    const channel = webChannel.channel_;
    assertNotNull(channel);

    simulateMessageEvent(channel, data);
    assertTrue(eventFired);
  }
@suppress {checkTypes} Allow sending a string as data, although not
supported by the method API, since it is done by clients.