Fix WebBluetooth generator to distinguish between different methods.

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 => 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.');