Import Cobalt 19.master.0.205881
diff --git a/src/base/system/system_monitor.h b/src/base/system/system_monitor.h
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+++ b/src/base/system/system_monitor.h
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+// 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 BASE_SYSTEM_SYSTEM_MONITOR_H_
+#define BASE_SYSTEM_SYSTEM_MONITOR_H_
+
+#include "base/base_export.h"
+#include "base/macros.h"
+#include "base/memory/ref_counted.h"
+#include "base/observer_list_threadsafe.h"
+#include "build/build_config.h"
+
+namespace base {
+
+// Class for monitoring various system-related subsystems
+// such as power management, network status, etc.
+// TODO(mbelshe): Add support beyond just power management.
+class BASE_EXPORT SystemMonitor {
+ public:
+ // Type of devices whose change need to be monitored, such as add/remove.
+ enum DeviceType {
+ DEVTYPE_AUDIO, // Audio device, e.g., microphone.
+ DEVTYPE_VIDEO_CAPTURE, // Video capture device, e.g., webcam.
+ DEVTYPE_UNKNOWN, // Other devices.
+ };
+
+ // Create SystemMonitor. Only one SystemMonitor instance per application
+ // is allowed.
+ SystemMonitor();
+ ~SystemMonitor();
+
+ // Get the application-wide SystemMonitor (if not present, returns NULL).
+ static SystemMonitor* Get();
+
+ class BASE_EXPORT DevicesChangedObserver {
+ public:
+ // Notification that the devices connected to the system have changed.
+ // This is only implemented on Windows currently.
+ virtual void OnDevicesChanged(DeviceType device_type) {}
+
+ protected:
+ virtual ~DevicesChangedObserver() = default;
+ };
+
+ // Add a new observer.
+ // Can be called from any thread.
+ // Must not be called from within a notification callback.
+ void AddDevicesChangedObserver(DevicesChangedObserver* obs);
+
+ // Remove an existing observer.
+ // Can be called from any thread.
+ // Must not be called from within a notification callback.
+ void RemoveDevicesChangedObserver(DevicesChangedObserver* obs);
+
+ // The ProcessFoo() style methods are a broken pattern and should not
+ // be copied. Any significant addition to this class is blocked on
+ // refactoring to improve the state of affairs. See http://crbug.com/149059
+
+ // Cross-platform handling of a device change event.
+ void ProcessDevicesChanged(DeviceType device_type);
+
+ private:
+ // Functions to trigger notifications.
+ void NotifyDevicesChanged(DeviceType device_type);
+
+ scoped_refptr<ObserverListThreadSafe<DevicesChangedObserver>>
+ devices_changed_observer_list_;
+
+ DISALLOW_COPY_AND_ASSIGN(SystemMonitor);
+};
+
+} // namespace base
+
+#endif // BASE_SYSTEM_SYSTEM_MONITOR_H_
