Add a NeededFrequency() method to the AudioMixer::Source interface.

webrtc/voice_engine/channel_proxy.h

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 79 matching lines @@
       GetAudioDecoderFactory() const;
 
   virtual void SetChannelOutputVolumeScaling(float scaling);
 
   virtual void SetRtcEventLog(RtcEventLog* event_log);
 
   virtual AudioMixer::Source::AudioFrameInfo GetAudioFrameWithInfo(
       int sample_rate_hz,
       AudioFrame* audio_frame);
 
+  virtual int NeededFrequency() const;
+
  private:
   Channel* channel() const;
 
   rtc::ThreadChecker thread_checker_;
   rtc::RaceChecker race_checker_;
   ChannelOwner channel_owner_;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(ChannelProxy);
 };
 }  // namespace voe
 }  // namespace webrtc
 
 #endif  // WEBRTC_VOICE_ENGINE_CHANNEL_PROXY_H_