Implement WebBluetooth getDescriptor[s]

third_party/WebKit/LayoutTests/bluetooth/script-tests/characteristic/descriptor-get-same-object.js

+'use strict';
+promise_test(() => {
+  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 => Promise.all([
+      characteristic.CALLS([
+        getDescriptor(user_description.alias),
+        getDescriptor(user_description.name),
+        getDescriptor(user_description.uuid)]),
+      characteristic.PREVIOUS_CALL]))
+    .then(descriptors_arrays => {
+
+      assert_true(descriptors_arrays.length > 0)
+
+      // Convert to arrays if necessary.
+      for (let i = 0; i < descriptors_arrays.length; i++) {
+        descriptors_arrays[i] = [].concat(descriptors_arrays[i]);
+      }
+
+      for (let i = 1; i < descriptors_arrays.length; i++) {
+        assert_equals(descriptors_arrays[0].length,
+                      descriptors_arrays[i].length);
+      }
+
+      let base_set = new Set(descriptors_arrays[0]);
+      for (let descriptors of descriptors_arrays) {
+        descriptors.forEach(
+          descriptor => assert_true(base_set.has(descriptor)));
+      }
+    });
+}, 'Calls to FUNCTION_NAME should return the same object.');