Implement WebBluetooth getDescriptor[s]

third_party/WebKit/LayoutTests/bluetooth/getDescriptor/get-same-Descriptor.html

Index: third_party/WebKit/LayoutTests/bluetooth/getDescriptor/get-same-Descriptor.html
diff --git a/third_party/WebKit/LayoutTests/bluetooth/notifications/concurrent-starts.html b/third_party/WebKit/LayoutTests/bluetooth/getDescriptor/get-same-Descriptor.html
similarity index 52%
copy from third_party/WebKit/LayoutTests/bluetooth/notifications/concurrent-starts.html
copy to third_party/WebKit/LayoutTests/bluetooth/getDescriptor/get-same-Descriptor.html
index 5f9b657fbeb31458543a171eb9f5b9f40df7b1d2..4248695f694e11de3c949680d79c761ecd1d165b 100644
--- a/third_party/WebKit/LayoutTests/bluetooth/notifications/concurrent-starts.html
+++ b/third_party/WebKit/LayoutTests/bluetooth/getDescriptor/get-same-Descriptor.html
@@ -4,18 +4,24 @@
 <script src="../../resources/bluetooth/bluetooth-helpers.js"></script>
 <script>
 'use strict';
+
 promise_test(() => {
   return setBluetoothFakeAdapter('HeartRateAdapter')
     .then(() => requestDeviceWithKeyDown({
-      filters: [{services: ['heart_rate']}]}))
+      filters: [{services: ['heart_rate']}],
+      optionalServices: ['generic_access']}))
     .then(device => device.gatt.connect())
     .then(gattServer => gattServer.getPrimaryService('heart_rate'))
     .then(service => service.getCharacteristic('heart_rate_measurement'))
     .then(characteristic => Promise.all([
-      characteristic.startNotifications(),
-      characteristic.startNotifications(),
-      characteristic.startNotifications()]));
-  // TODO(ortuno): Assert that notifications are active.
-  // http://crbug.com/600762
-}, 'Multiple starts in a row.');
+      characteristic.getDescriptor(user_description.alias),
+      characteristic.getDescriptor(user_description.alias)])
+    .then(descriptors => {
+      for (var i = 1; i < descriptors.length; i++) {
+        assert_not_equals(
+          descriptors[0], descriptors[i],
+          'Should return the same descriptor as the first call.');
+      }
+    }))
+}, 'Calls to get the same descriptor should return the same object.');
 </script>