bluetooth: Better disconnected error messages for GATT operations.

third_party/WebKit/LayoutTests/bluetooth/script-tests/descriptor/io-op-garbage-collection-ran-during-success.js

 'use strict';
 promise_test(
     () => {
       let val = new Uint8Array([1]);
       let promise;
       return setBluetoothFakeAdapter('DisconnectingHealthThermometerAdapter')
           .then(
               () => requestDeviceWithKeyDown(
                   {filters: [{services: ['health_thermometer']}]}))
           .then(device => device.gatt.connect())
           .then(
               gattServer => gattServer.getPrimaryService('health_thermometer'))
           .then(service => service.getCharacteristic('measurement_interval'))
           .then(
               characteristic =>
                   characteristic.getDescriptor(user_description.name))
           .then(descriptor => {
             promise = assert_promise_rejects_with_message(
                 descriptor.CALLS([readValue()|writeValue(val)]),
                 new DOMException(
-                    'GATT Server disconnected while performing a GATT operation.',
+                  'GATT Server is disconnected. Cannot perform GATT operations. ' +
+                    '(Re)connect first with `device.gatt.connect`.',
                     'NetworkError'));
             // Disconnect called to clear attributeInstanceMap and allow the
             // object to get garbage collected.
             descriptor.characteristic.service.device.gatt.disconnect();
           })
           .then(runGarbageCollection)
           .then(() => promise);
     },
     'Garbage collection ran during a FUNCTION_NAME call that succeeds. ' +
         'Should not crash.');