Fix WebBluetooth generator to distinguish between different methods.

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(() => get_request_disconnection(gattServer))
-        .then(requestDisconnection => requestDisconnection())
-        .then(() => assert_promise_rejects_with_message(
-          measurement_interval.CALLS([
-            readValue()|
-            writeValue(val)|
-            startNotifications()|
-            stopNotifications()]),
-          new DOMException(
-            'GATT Server is disconnected. Cannot perform GATT operations.',
-            'NetworkError')));
-    });
-}, 'Device disconnects before FUNCTION_NAME. Reject with NetworkError.');