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 connections may occur if subsequent requests are
+ * made before the first request is resolved. In this case, the connection is
+ * dropped.
+ */
+
+// Expose for testing.
+/** @type {!Map<string, !interfaces.BluetoothDevice.DevicePtr>} */
+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
+   * DeviceBroker.
+   * @param {string} address
+   * @return {!Promise<!DeviceBroker>}
+   */
+  function connectToDevice(address) {
+    if (connectedDevices.has(address))

[dpapad, 2017/01/19 02:01:47]

Is this function meant to call adapterBroker.connectToDevice once, and simply
return the same promise for a 2nd connection request (while the 1st one is
already in-flight)? Currently there is a race condition if it gets called twice
in a row for the same device.

If that is the case, instead of checking a map of connectedDevices, we should be
keeping track of promises instead (such that you can return the previously
constructed promise, even if the device has not connected yet).

[mbrunson, 2017/01/19 03:22:20]

I was less concerned about connection requests in flight and more about
returning the same Device. I have cached the promise here to catch redundant
connection requests as well.

+      return Promise.resolve(connectedDevices.get(address));
+
+    return adapter_broker.getAdapterBroker().then(function(adapterBroker) {

[dpapad, 2017/01/19 02:01:47]

Chain instead of nesting, as follows

  ...
  return adapter_broker.getAdapterBroker();
}).then(function(adapterBroker) {
  return adapterBroker.connectToDevice(address);
}).then(....)

[mbrunson, 2017/01/19 03:22:20]

What function is "return adapter_broker.getAdapterBroker();" in. There's no
chain there.

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

Ack. I misread the diff.

+      return adapterBroker.connectToDevice(address);
+    }).then(function(device) {
+      // If multiple connections occur, only use the first active connection.
+      if (connectedDevices.has(address)) {
+        device.disconnect();
+        return connectedDevices.get(address);
+      }
+
+      device.ptr.setConnectionErrorHandler(function() {
+        connectedDevices.delete(address);
+      });
+
+      connectedDevices.set(address, device);
+      return device;
+    });
+  }
+
+  return {
+    connectToDevice: connectToDevice
+  };
+});