Adding key press detection in the browser process.

media/audio/key_press_monitor.h

+// Copyright (c) 2013 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 MEDIA_AUDIO_KEY_PRESS_MONITOR_H_
+#define MEDIA_AUDIO_KEY_PRESS_MONITOR_H_
+
+#include "base/basictypes.h"
+#include "base/observer_list.h"
+#include "base/synchronization/lock.h"
+
+namespace media {
+
+// This class monitors the system-wide key presses and notifies the listeners.
+// All methods can be called on any thread.
+// TODO(jiayl): this is only a stub now. Need to implement the event monitoring.
+class KeyPressMonitor {
+ public:
+  // The implementation has to be thread safe.
+  class KeyPressListener {
+   public:
+    // This can be called on any thread.
+    virtual void OnKeyPressed() = 0;
+   protected:
+    virtual ~KeyPressListener() {}
+  };
+
+  KeyPressMonitor();
+  ~KeyPressMonitor();
+
+  // Adds |listener| to receive event notifications. A listener should not be
+  // added more than once.
+  // The callers should make sure |listener| is valid and call
+  // RemoveKeyPressListener before |listener| is destroyed.
+  void AddKeyPressListener(KeyPressListener* listener);
+  // Removes |listener| from receiving event notifications. Does nothing if
+  // |listener| has not been added or has already been removed.
+  void RemoveKeyPressListener(KeyPressListener* listener);
+
+ private:
+  // Raw pointers of the listeners.
+  typedef ObserverList<KeyPressListener> ListenerList;

[DaleCurtis, 2013/08/02 01:01:17]

Typedef seems a bit overkill.  AudioInputController will always call Add/Remove
on the audio thread, you should be able to remove the Lock and just use a
base::ThreadChecker for sanity.  Is anyone else expected to call these methods?

[jiayl, 2013/08/02 20:32:20]

Done.

+  ListenerList listeners_;
+  base::Lock listeners_lock_;
+
+  DISALLOW_COPY_AND_ASSIGN(KeyPressMonitor);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_KEY_PRESS_MONITOR_H_