add device monitoring on Mac.

content/browser/device_monitor_mac.h

+// Copyright (c) 2012 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_DEVICE_MONITOR_MAC_H_
+#define CONTENT_BROWSER_DEVICE_MONITOR_MAC_H_
+
+#include <IOKit/IOKitLib.h>
+
+#include "base/basictypes.h"
+
+namespace content {
+
+class DeviceMonitorMac {
+ public:
+  DeviceMonitorMac();
+  ~DeviceMonitorMac();
+
+ private:
+  void RegisterCallbacks(IONotificationPortRef port);
+
+  // Do we need UnregisterCallbacks()?
+
+  DISALLOW_COPY_AND_ASSIGN(DeviceMonitorMac);
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_DEVICE_MONITOR_MAC_H_