Move getUserMedia finish to "when audio track configured".

content/renderer/media/media_stream_audio_track.h

Index: content/renderer/media/media_stream_audio_track.h
diff --git a/content/renderer/media/media_stream_audio_track.h b/content/renderer/media/media_stream_audio_track.h
index f5fa754787f80b3ec34b8651276e49d3dd054678..8e049c1e228a2ff6b8f72899353e6f7fcfd11b54 100644
--- a/content/renderer/media/media_stream_audio_track.h
+++ b/content/renderer/media/media_stream_audio_track.h
@@ -8,6 +8,7 @@
 #include <memory>
 
 #include "base/atomicops.h"
+#include "base/bind.h"
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
@@ -72,6 +73,11 @@ class CONTENT_EXPORT MediaStreamAudioTrack : public MediaStreamTrack {
   // method to provide safe down-casting to their type.
   virtual void* GetClassIdentifier() const;
 
+  void SetFormatConfiguredCallback(base::OnceCallback<void()> callback) {
+    base::AutoLock guard(format_set_guard_);
+    format_set_callback_ = std::move(callback);
+  }
+
  private:
   friend class MediaStreamAudioSource;
   friend class MediaStreamAudioDeliverer<MediaStreamAudioTrack>;
@@ -95,6 +101,8 @@ class CONTENT_EXPORT MediaStreamAudioTrack : public MediaStreamTrack {
   void getSettings(blink::WebMediaStreamTrack::Settings& settings) override;
 
  private:
+  bool format_is_set();
+
   // In debug builds, check that all methods that could cause object graph
   // or data flow changes are being called on the main thread.
   base::ThreadChecker thread_checker_;
@@ -111,6 +119,11 @@ class CONTENT_EXPORT MediaStreamAudioTrack : public MediaStreamTrack {
   // Buffer used to deliver silent audio data while this track is disabled.
   std::unique_ptr<media::AudioBus> silent_bus_;
 
+  // True if the track knows its configuration (OnSetFormat has been called).
+  bool format_is_set_ = false;
+  base::OnceCallback<void()> format_set_callback_;
+  base::Lock format_set_guard_;
+
   // Provides weak pointers that are valid until Stop() is called.
   base::WeakPtrFactory<MediaStreamAudioTrack> weak_factory_;