Fixed the crash in the wbaudio source provider when the audio track is going away.

Source/modules/webaudio/AudioContext.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 419 matching lines @@
                 "invalid MediaStream source"));
         return 0;
     }
 
     ASSERT(isMainThread());
     lazyInitialize();
 
     AudioSourceProvider* provider = 0;
 
     MediaStreamTrackVector audioTracks = mediaStream->getAudioTracks();
+    RefPtr<MediaStreamTrack> audioTrack;
 
     // FIXME: get a provider for non-local MediaStreams (like from a remote peer).
     for (size_t i = 0; i < audioTracks.size(); ++i) {
-        RefPtr<MediaStreamTrack> localAudio = audioTracks[i];
-        if (localAudio->component()->audioSourceProvider()) {
-            provider = localAudio->component()->audioSourceProvider();
+        audioTrack = audioTracks[i];
+        if (audioTrack->component()->audioSourceProvider()) {
+            provider = audioTrack->component()->audioSourceProvider();
             break;
         }
     }
 
-    RefPtr<MediaStreamAudioSourceNode> node = MediaStreamAudioSourceNode::create(this, mediaStream, provider);
+    RefPtr<MediaStreamAudioSourceNode> node = MediaStreamAudioSourceNode::create(this, mediaStream, audioTrack.get(), provider);
 
     // FIXME: Only stereo streams are supported right now. We should be able to accept multi-channel streams.
     node->setFormat(2, sampleRate());
 
     refNode(node.get()); // context keeps reference until node is disconnected
     return node;
 }
 
 PassRefPtr<MediaStreamAudioDestinationNode> AudioContext::createMediaStreamDestination()
 {
@@ skipping 640 matching lines @@
 }
 
 void AudioContext::decrementActiveSourceCount()
 {
     atomicDecrement(&m_activeSourceCount);
 }
 
 } // namespace WebCore
 
 #endif // ENABLE(WEB_AUDIO)