bluetooth: Introduce helper function for requesting a disconnection

third_party/WebKit/LayoutTests/bluetooth/script-tests/service-device-disconnects-before.js

 'use strict';
 promise_test(t => {
   return setBluetoothFakeAdapter('DisconnectingHeartRateAdapter')
     .then(() => requestDeviceWithKeyDown({
       filters: [{services: ['heart_rate']}],
       optionalServices: [request_disconnection_service_uuid]
     }))
     .then(device => {
       return device.gatt.connect()
-        .then(gattServer => gattServer.getPrimaryService(
-          request_disconnection_service_uuid))
-        .then(service => service.getCharacteristic(
-          request_disconnection_characteristic_uuid))
-        .then(requestDisconnection => requestDisconnection.writeValue(
-          new Uint8Array([0])))
+        .then(gattServer => get_request_disconnection(gattServer))
+        .then(requestDisconnection => requestDisconnection())
         .then(() => assert_promise_rejects_with_message(
           device.gatt.CALLS([
             getPrimaryService('heart_rate')|
             getPrimaryServices()|
             getPrimaryServices('heart_rate')[UUID]]),
           new DOMException(
             'GATT Server is disconnected. Cannot retrieve services.',
             'NetworkError')));
     });
 }, 'Device disconnects before FUNCTION_NAME. Reject with NetworkError.');