Revert of MediaStream audio object graph untangling and clean-ups.

content/renderer/media/webaudio_capturer_source.h

Index: content/renderer/media/webaudio_capturer_source.h
diff --git a/content/renderer/media/webaudio_capturer_source.h b/content/renderer/media/webaudio_capturer_source.h
index f127de3aa2fbdc1f753fb89e4e698be283c04ad2..d5b3bb5b554514d8d75ee909bf8ab23f63914279 100644
--- a/content/renderer/media/webaudio_capturer_source.h
+++ b/content/renderer/media/webaudio_capturer_source.h
@@ -8,6 +8,7 @@
 #include <stddef.h>
 
 #include "base/macros.h"
+#include "base/memory/ref_counted.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/thread_checker.h"
 #include "base/time/time.h"
@@ -30,11 +31,12 @@
 //    (channels, and sample-rate).
 // 2. consumeAudio() is called periodically by WebKit which dispatches the
 //    audio stream to the WebRtcLocalAudioTrack::Capture() method.
-class WebAudioCapturerSource : public blink::WebAudioDestinationConsumer {
+class WebAudioCapturerSource
+    :  public base::RefCountedThreadSafe<WebAudioCapturerSource>,
+       public blink::WebAudioDestinationConsumer {
  public:
-  explicit WebAudioCapturerSource(blink::WebMediaStreamSource* blink_source);
-
-  ~WebAudioCapturerSource() override;
+  explicit WebAudioCapturerSource(
+      const blink::WebMediaStreamSource& blink_source);
 
   // WebAudioDestinationConsumer implementation.
   // setFormat() is called early on, so that we can configure the audio track.
@@ -45,12 +47,17 @@
                     size_t number_of_frames) override;
 
   // Called when the WebAudioCapturerSource is hooking to a media audio track.
-  // |track| is the sink of the data flow and must remain alive until Stop() is
-  // called.
+  // |track| is the sink of the data flow. |source_provider| is the source of
+  // the data flow where stream information like delay, volume, key_pressed,
+  // is stored.
   void Start(WebRtcLocalAudioTrack* track);
 
   // Called when the media audio track is stopping.
   void Stop();
+
+ protected:
+  friend class base::RefCountedThreadSafe<WebAudioCapturerSource>;
+  ~WebAudioCapturerSource() override;
 
  private:
   // Called by AudioPushFifo zero or more times during the call to
@@ -59,13 +66,16 @@
   void DeliverRebufferedAudio(const media::AudioBus& audio_bus,
                               int frame_delay);
 
-  // Deregisters this object from its blink::WebMediaStreamSource.
-  void DeregisterFromBlinkSource();
+  // Removes this object from a blink::WebMediaStreamSource with which it
+  // might be registered. The goal is to avoid dangling pointers.
+  void removeFromBlinkSource();
 
   // Used to DCHECK that some methods are called on the correct thread.
   base::ThreadChecker thread_checker_;
 
   // The audio track this WebAudioCapturerSource is feeding data to.
+  // WebRtcLocalAudioTrack is reference counted, and owning this object.
+  // To avoid circular reference, a raw pointer is kept here.
   WebRtcLocalAudioTrack* track_;
 
   media::AudioParameters params_;