Pass through audio if HRTF database isn't loaded yet.

third_party/WebKit/Source/modules/webaudio/PannerNode.cpp

 /*
  * 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 116 matching lines @@
     }
 
     // The audio thread can't block on this lock, so we call tryLock() instead.
     MutexTryLocker tryLocker(m_processLock);
     MutexTryLocker tryListenerLocker(listener()->listenerLock());
 
     if (tryLocker.locked() && tryListenerLocker.locked()) {
         // HRTFDatabase should be loaded before proceeding when the panning model is HRTF.
         if (m_panningModel == Panner::PanningModelHRTF && !listener()->isHRTFDatabaseLoaded()) {
             if (context()->hasRealtimeConstraint()) {
-                // Some BaseAudioContexts cannot block on the HRTFDatabase loader.
-                destination->zero();
+                // Realtime AudioContext's cannot block on the HRTFDatabase
+                // loader.  Instead, copy the input to the output so we can at
+                // least hear something until the database is ready.
+                destination->copyFrom(*source, m_channelInterpretation);
                 return;
             }
 
             listener()->waitForHRTFDatabaseLoaderThreadCompletion();
         }
 
         if (hasSampleAccurateValues() || listener()->hasSampleAccurateValues()) {
             // It's tempting to skip sample-accurate processing if isAzimuthElevationDirty() and
             // isDistanceConeGain() both return false.  But in general we can't because something
             // may scheduled to start in the middle of the rendering quantum.  On the other hand,
@@ skipping 631 matching lines @@
     visitor->trace(m_positionZ);
 
     visitor->trace(m_orientationX);
     visitor->trace(m_orientationY);
     visitor->trace(m_orientationZ);
 
     AudioNode::trace(visitor);
 }
 
 } // namespace blink