Avoid AudioBufferSourceHandler data race.

third_party/WebKit/Source/modules/webaudio/AudioBufferSourceNode.h

 /*
  * Copyright (C) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 150 matching lines @@
   bool is_grain_;
   double grain_offset_;    // in seconds
   double grain_duration_;  // in seconds
   // True if grainDuration is given explicitly (via 3 arg start method).
   bool is_duration_given_;
 
   // Compute playback rate (k-rate) by incorporating the sample rate
   // conversion factor, and the value of playbackRate and detune AudioParams.
   double ComputePlaybackRate();
 
+  double GetMinPlaybackRate();
+
   // The minimum playbackRate value ever used for this source.
   double min_playback_rate_;
+
+  // |min_playback_rate_| may be updated by the audio thread
+  // while the main thread checks if the node is in a stoppable
+  // state, hence access needs to be atomic.
+  //
+  // TODO: when the codebase adopts std::atomic<>, use it for
+  // |min_playback_rate_|.
+  Mutex min_playback_rate_mutex_;
 };
 
 class AudioBufferSourceNode final : public AudioScheduledSourceNode {
   DEFINE_WRAPPERTYPEINFO();
 
  public:
   static AudioBufferSourceNode* Create(BaseAudioContext&, ExceptionState&);
   static AudioBufferSourceNode* Create(BaseAudioContext*,
                                        AudioBufferSourceOptions&,
                                        ExceptionState&);
@@ skipping 22 matching lines @@
  private:
   AudioBufferSourceNode(BaseAudioContext&);
 
   Member<AudioParam> playback_rate_;
   Member<AudioParam> detune_;
 };
 
 }  // namespace blink
 
 #endif  // AudioBufferSourceNode_h