bluetooth: Add characteristic list to DeviceDetailsPage in internals page.

chrome/browser/resources/bluetooth_internals/device_broker.js

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/**
+ * Javascript for device_broker, served from chrome://bluetooth-internals/.
+ * Provides a single source to access DevicePtrs. DevicePtrs are cached for
+ * for repeated use. Multiple connection requests will result in the same
+ * DevicePtr being shared among all requesters.
+ */
+
+// Expose for testing.
+/** @type {!Map<string, !interfaces.BluetoothDevice.DevicePtr|!Promise} */
+var connectedDevices = null;
+
+cr.define('device_broker', function() {
+  connectedDevices = new Map();
+
+  /**
+   * Creates a GATT connection to the device with |address|. If a connection to
+   * the device already exists, the promise is resolved with the existing
+   * DevicePtr. If a connection is in progress, the promise resolves when
+   * the existing connection request promise is fulfilled.
+   * @param {string} address
+   * @return {!Promise<!interfaces.BluetoothDevice.DevicePtr>}
+   */
+  function connectToDevice(address) {

[dpapad, 2017/01/19 17:41:45]

Nit (optional): You can avoid querying the map twice as follows:

var deviceOrPromise = connectedDevices.get(address) || null;
if (deviceOrPromise !== null)
  return Promise.resolve(deviceOrPromise);

[mbrunson, 2017/01/19 23:34:10]

Done.

+    if (connectedDevices.has(address))
+      return Promise.resolve(connectedDevices.get(address));
+
+    var promise = adapter_broker.getAdapterBroker().then(
+        function(adapterBroker) {
+          return adapterBroker.connectToDevice(address);
+        }).then(function(device) {
+          connectedDevices.set(address, device);
+
+          device.ptr.setConnectionErrorHandler(function() {
+            connectedDevices.delete(address);
+          });
+
+          return device;
+        }).catch(function(error) {
+          connectedDevices.delete(address);
+          throw error;
+        });
+
+    connectedDevices.set(address, promise);
+    return promise;
+  }
+
+  return {
+    connectToDevice: connectToDevice
+  };
+});