Clear DeferredTaskHandler's audio thread ID upon the thread going away.

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

Index: third_party/WebKit/Source/modules/webaudio/AudioContext.cpp
diff --git a/third_party/WebKit/Source/modules/webaudio/AudioContext.cpp b/third_party/WebKit/Source/modules/webaudio/AudioContext.cpp
index e45fbf22d878e21d2aca2e1e491cee4fa2fc6e2d..558e122878be9cfde49f2c2f3ae1a0ffad95b817 100644
--- a/third_party/WebKit/Source/modules/webaudio/AudioContext.cpp
+++ b/third_party/WebKit/Source/modules/webaudio/AudioContext.cpp
@@ -194,6 +194,10 @@ void AudioContext::stopRendering()
         destination()->audioDestinationHandler().stopRendering();
         setContextState(Suspended);
         deferredTaskHandler().clearHandlersToBeDeleted();
+        // The recorded audio thread will be shut down as part
+        // of stopping, so clear that association to avoid
+        // future confusion (crbug.com/612127)
+        deferredTaskHandler().clearAudioThread();
     }
 }