bluetooth: Better disconnected error messages for characteristic retrieval.

third_party/WebKit/LayoutTests/bluetooth/script-tests/service/garbage-collection-ran-during-error.js

 'use strict';
 promise_test(() => {
   let promise;
   return setBluetoothFakeAdapter('MissingCharacteristicHeartRateAdapter')
     .then(() => requestDeviceWithKeyDown({
       filters: [{services: ['heart_rate']}]}))
     .then(device => device.gatt.connect())
     .then(gattServer => gattServer.getPrimaryService('heart_rate'))
     .then(service => {
       promise = assert_promise_rejects_with_message(
         service.CALLS([
           getCharacteristic('measurement_interval')|
           getCharacteristics()|
           getCharacteristics('measurement_interval')[UUID]]),
         new DOMException(
-          'GATT Server disconnected while retrieving characteristics.',
+          'GATT Server is disconnected. Cannot retrieve characteristics. ' +
+          '(Re)connect first with `device.gatt.connect`.',
           'NetworkError'));
       // Disconnect called to clear attributeInstanceMap and allow the
       // object to get garbage collected.
       service.device.gatt.disconnect();
     })
     .then(runGarbageCollection)
     .then(() => promise);
 }, 'Garbage Collection ran during FUNCTION_NAME call that fails. ' +
    'Should not crash');