bluetooth: Better disconnected error messages for GATT operations.

third_party/WebKit/LayoutTests/resources/bluetooth/bluetooth-helpers.js

 'use strict';
 
 // Bluetooth UUID constants:
 // Services:
 var blocklist_test_service_uuid = "611c954a-263b-4f4a-aab6-01ddb953f985";
 var request_disconnection_service_uuid = "01d7d889-7451-419f-aeb8-d65e7b9277af";
 // Characteristics:
 var blocklist_exclude_reads_characteristic_uuid =
   "bad1c9a2-9a5b-4015-8b60-1579bbbf2135";
 var request_disconnection_characteristic_uuid =
@@ skipping 350 matching lines @@
 //   .then(gatt => get_request_disconnection(gatt))
 //   .then(requestDisconnection => requestDisconnection())
 //   .then(() => // device is now disconnected)
 function get_request_disconnection(gattServer) {
   return gattServer.getPrimaryService(request_disconnection_service_uuid)
     .then(service => service.getCharacteristic(request_disconnection_characteristic_uuid))
     .then(characteristic => {
       return () => assert_promise_rejects_with_message(
         characteristic.writeValue(new Uint8Array([0])),
         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'));
     });
 }
 
 function generateRequestDeviceArgsWithServices(services = ['heart_rate']) {
   return [{
     filters: [{ services: services }]
   }, {
     filters: [{ services: services, name: 'Name' }]
   }, {
     filters: [{ services: services, namePrefix: 'Pre' }]
   }, {
     filters: [{ services: services, name: 'Name', namePrefix: 'Pre' }]
   }, {
     filters: [{ services: services }],
     optionalServices: ['heart_rate']
   }, {
     filters: [{ services: services, name: 'Name' }],
     optionalServices: ['heart_rate']
   }, {
     filters: [{ services: services, namePrefix: 'Pre' }],
     optionalServices: ['heart_rate']
   }, {
     filters: [{ services: services, name: 'Name', namePrefix: 'Pre' }],
     optionalServices: ['heart_rate']
   }];
 }