bluetooth: Introduce helper function for requesting a disconnection

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

 'use strict';
 promise_test(() => {
   let val = new Uint8Array([1]);
   return setBluetoothFakeAdapter('DisconnectingHealthThermometerAdapter')
     .then(() => requestDeviceWithKeyDown({
       filters: [{services: ['health_thermometer']}],
       optionalServices: [request_disconnection_service_uuid]
     }))
     .then(device => device.gatt.connect())
     .then(gattServer => {
       let measurement_interval;
       return gattServer.getPrimaryService('health_thermometer')
         .then(ht=> ht.getCharacteristic('measurement_interval'))
         .then(mi => measurement_interval = mi)
-        .then(() => gattServer.getPrimaryService(
-          request_disconnection_service_uuid))
-        .then(service => service.getCharacteristic(
-          request_disconnection_characteristic_uuid))
-        .then(requestDisconnection => requestDisconnection.writeValue(
-          new Uint8Array([0])))
+        .then(() => get_request_disconnection(gattServer))
+        .then(requestDisconnection => requestDisconnection())
         .then(() => assert_promise_rejects_with_message(
           measurement_interval.CALLS([readValue()]),
           new DOMException(
             'GATT Server is disconnected. Cannot perform GATT operations.',
             'NetworkError')));
     });
 }, 'Device disconnects before FUNCTION_NAME. Reject with NetworkError.');