Keep track of the user-facing number of channels in a ChannelBuffer

webrtc/modules/audio_processing/audio_buffer.h

Index: webrtc/modules/audio_processing/audio_buffer.h
diff --git a/webrtc/modules/audio_processing/audio_buffer.h b/webrtc/modules/audio_processing/audio_buffer.h
index d90219e91331ac0d9547cb2557408bcbd487d40d..d0e79db3293c790d7dfd7504f3e6d58f32fff3c1 100644
--- a/webrtc/modules/audio_processing/audio_buffer.h
+++ b/webrtc/modules/audio_processing/audio_buffer.h
@@ -123,6 +123,8 @@ class AudioBuffer {
   void MergeFrequencyBands();
 
  private:
+  FRIEND_TEST_ALL_PREFIXES(AudioBufferTest,
+                           SetNumChannelsSetsChannelBuffersNumChannels);
   // Called from DeinterleaveFrom() and CopyFrom().
   void InitForNewData();