MediaStream audio object graph untangling and clean-ups.

content/renderer/media/media_stream_audio_level_calculator.h

Index: content/renderer/media/media_stream_audio_level_calculator.h
diff --git a/content/renderer/media/media_stream_audio_level_calculator.h b/content/renderer/media/media_stream_audio_level_calculator.h
index e7d25cc5d548add19f02afa9b35796f20e0ca7ca..af9bdc88cbe8ac21e54a857f1297a4383bb6eff4 100644
--- a/content/renderer/media/media_stream_audio_level_calculator.h
+++ b/content/renderer/media/media_stream_audio_level_calculator.h
@@ -5,7 +5,9 @@
 #ifndef CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_LEVEL_CALCULATOR_H_
 #define CONTENT_RENDERER_MEDIA_MEDIA_STREAM_AUDIO_LEVEL_CALCULATOR_H_
 
-#include "base/threading/thread_checker.h"
+#include "base/memory/ref_counted.h"
+#include "base/synchronization/lock.h"
+#include "content/common/content_export.h"
 
 namespace media {
 class AudioBus;
@@ -13,30 +15,49 @@ class AudioBus;
 
 namespace content {
 
-// This class is used by the WebRtcLocalAudioTrack to calculate the level of
-// the audio signal. And the audio level will be eventually used by the volume
+// This class is used by the WebRtcAudioCapturer to calculate the level of the
+// audio signal. And the audio level will be eventually used by the volume
 // animation UI.
+//
 // The algorithm used by this class is the same as how it is done in
 // third_party/webrtc/voice_engine/level_indicator.cc.
-class MediaStreamAudioLevelCalculator {
+class CONTENT_EXPORT MediaStreamAudioLevelCalculator {
  public:
+  // Provides thread-safe access to the current signal level.  This object is
+  // intended to be passed to modules running on other threads that poll for the
+  // current signal level.
+  class Level : public base::RefCountedThreadSafe<Level> {
+   public:
+    float GetCurrent() const;
+
+   private:
+    friend class MediaStreamAudioLevelCalculator;
+    friend class base::RefCountedThreadSafe<Level>;
+
+    Level();
+    ~Level();
+
+    void Set(float level);
+
+    mutable base::Lock lock_;
+    float level_;
+  };
+
   MediaStreamAudioLevelCalculator();
   ~MediaStreamAudioLevelCalculator();
 
-  // Calculates the signal level of the audio data, returning the absolute value
-  // of the amplitude of the signal.
-  float Calculate(const media::AudioBus& audio_bus);
+  scoped_refptr<Level> level() const { return level_; }
 
- private:
-  // Used to DCHECK that the constructor and Calculate() are always called on
-  // the same audio thread. Note that the destructor will be called on a
-  // different thread, which can be either the main render thread or a new
-  // audio thread where WebRtcLocalAudioTrack::OnSetFormat() is called.
-  base::ThreadChecker thread_checker_;
+  // Scans the audio signal in |audio_bus| and computes a new signal level
+  // exposed by Level.  If |assume_nonzero_energy| is true, then a completely
+  // zero'ed-out |audio_bus| will be accounted for as having a very faint,
+  // non-zero level.
+  void Calculate(const media::AudioBus& audio_bus, bool assume_nonzero_energy);
 
+ private:
   int counter_;
   float max_amplitude_;
-  float level_;
+  const scoped_refptr<Level> level_;
 };
 
 }  // namespace content