Fix WebBluetooth generator to distinguish between different methods.

third_party/WebKit/LayoutTests/bluetooth/script-tests/characteristic/gatt-op-device-disconnects-during-success.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 => {
@@ skipping 11 matching lines @@
               writeValue(val)|
               startNotifications()|
               stopNotifications()]),
             new DOMException(
               'GATT Server disconnected while performing a GATT operation.',
               'NetworkError'));
         });
     });
 }, 'Device disconnects during a FUNCTION_NAME call that succeeds. ' +
    'Reject with NetworkError.');