refactor AudioInputDevice to remove race condition.

content/renderer/media/audio_input_device_event_handler.h

+// Copyright (c) 2011 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_RENDERER_MEDIA_AUDIO_INPUT_DEVICE_EVENT_HANDLER_H_
+#define CONTENT_RENDERER_MEDIA_AUDIO_INPUT_DEVICE_EVENT_HANDLER_H_
+
+class AudioInputDeviceEventHandler {
+ public:
+  // Audio recording has been started.
+  virtual void OnRecordingStarted() = 0;
+
+  // Audio recording has been stopped.
+  virtual void OnRecordingStopped() = 0;
+
+ protected:
+  virtual ~AudioInputDeviceEventHandler() {}
+};
+
+#endif  // CONTENT_RENDERER_MEDIA_AUDIO_INPUT_DEVICE_EVENT_HANDLER_H_