[Chromoting] Add AudioVolumeApplier to reduce the complexity and the dependency of kChannels

remoting/host/audio_silence_detector.h

Index: remoting/host/audio_silence_detector.h
diff --git a/remoting/host/audio_silence_detector.h b/remoting/host/audio_silence_detector.h
index 95fd6546bac5a71fe93f0a1dad483ce6ba088e1f..3e7a05bf16fabc5c2796c24c954a00a358357222 100644
--- a/remoting/host/audio_silence_detector.h
+++ b/remoting/host/audio_silence_detector.h
@@ -24,7 +24,10 @@ class AudioSilenceDetector {
 
   // Must be called for each new chunk of data. Return true the given packet
   // is silence should be dropped.
-  bool IsSilence(const int16_t* samples, size_t samples_count);
+  bool IsSilence(const int16_t* samples, size_t frames);
+
+  // The count of channels received from last Reset().
+  int channels() const;
 
  private:
   // Maximum absolute sample value that should still be considered as silence.
@@ -37,6 +40,9 @@ class AudioSilenceDetector {
 
   // Lengths of the current silence period in samples.
   int silence_length_;
+
+  // The count of channels.
+  int channels_;
 };
 
 }  // namespace remoting