Add Media device notification to SystemMonitor and Mac impl

content/browser/mac/media_device_notifications.h

Index: content/browser/mac/media_device_notifications.h
diff --git a/content/browser/mac/media_device_notifications.h b/content/browser/mac/media_device_notifications.h
new file mode 100644
index 0000000000000000000000000000000000000000..e96fdc6cee6463fff913674f151a5a7c4d6ccb89
--- /dev/null
+++ b/content/browser/mac/media_device_notifications.h
@@ -0,0 +1,15 @@
+// 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_MAC_MEDIA_DEVICE_NOTIFICATIONS_H_
+#define CONTENT_BROWSER_MAC_MEDIA_DEVICE_NOTIFICATIONS_H_
+#pragma once
+
+namespace content {
+
+void StartMediaDeviceNotifications();
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_MAC_MEDIA_DEVICE_NOTIFICATIONS_H_