Add UMA for the number of devices in the chooser when a device is paired

content/browser/bluetooth/bluetooth_device_chooser_controller.h

 // Copyright 2016 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.
 
 #ifndef CONTENT_BROWSER_BLUETOOTH_BLUETOOTH_DEVICE_CHOOSER_CONTROLLER_H_
 #define CONTENT_BROWSER_BLUETOOTH_BLUETOOTH_DEVICE_CHOOSER_CONTROLLER_H_
 
 #include <string>
+#include <unordered_set>
 
 #include "base/memory/weak_ptr.h"
 #include "base/optional.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/bluetooth_chooser.h"
 #include "third_party/WebKit/public/platform/modules/bluetooth/web_bluetooth.mojom.h"
 
 namespace device {
@@ skipping 123 matching lines @@
 
   // The last discovery session to be started.
   // TODO(ortuno): This should be null unless there is an active discovery
   // session. We need to null it when the platform stops discovery.
   // http://crbug.com/611852
   std::unique_ptr<device::BluetoothDiscoverySession> discovery_session_;
 
   // The time when scanning starts.
   base::Optional<base::TimeTicks> scanning_start_time_;
 
+  // The device ids that are currently shown in the chooser.
+  std::unordered_set<std::string> device_ids_;
+
   // Weak pointer factory for generating 'this' pointers that might live longer
   // than we do.
   // Note: This should remain the last member so it'll be destroyed and
   // invalidate its weak pointers before any other members are destroyed.
   base::WeakPtrFactory<BluetoothDeviceChooserController> weak_ptr_factory_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_BLUETOOTH_BLUETOOTH_DEVICE_CHOOSER_CONTROLLER_H_