The following layout test fails when moving it over to the new framework:

https://cs.chromium.org/chromium/src/third_party/WebKit/LayoutTests/bluetooth/characteristic/notifications/concurrent-starts.html?type=cs&q=concurrent-starts.h&sq=package:chromium&l=1

'use strict';
promise_test(() => {
  return setBluetoothFakeAdapter('HeartRateAdapter')
    .then(() => requestDeviceWithKeyDown({
      filters: [{services: ['heart_rate']}]}))
    .then(device => device.gatt.connect())
    .then(gattServer => gattServer.getPrimaryService('heart_rate'))
    .then(service => service.getCharacteristic('heart_rate_measurement'))
    .then(characteristic => Promise.all([
      characteristic.startNotifications(),
      characteristic.startNotifications(),
      characteristic.startNotifications()]));
  // TODO(ortuno): Assert that notifications are active.
  // http://crbug.com/600762
}, 'Multiple starts in a row.');

It seems that after the startNotifications calls the end state is "Not subscribed". Probably a problem with how we do queuing in the underlying layer, currently writing a device_unittest to check.