Verify executionContext() exists before trying to print message.

Source/modules/webaudio/MediaElementAudioSourceNode.cpp

 /*
  * Copyright (C) 2011, 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 157 matching lines @@
                 m_multiChannelResampler->process(provider, outputBus, numberOfFrames);
             } else {
                 // Bypass the resampler completely if the source is at the context's sample-rate.
                 ASSERT(m_sourceSampleRate == sampleRate());
                 provider->provideInput(outputBus, numberOfFrames);
             }
             // Output silence if we don't have access to the element.
             if (!passesCORSAccessCheck()) {
                 if (m_maybePrintCORSMessage) {
                     // Print a CORS message, but just once for each change in the current media
-                    // element source.
+                    // element source, and only if we have a document to print to.
                     m_maybePrintCORSMessage = false;
-                    context()->executionContext()->postTask(FROM_HERE,
-                        createCrossThreadTask(&MediaElementAudioSourceHandler::printCORSMessage,
-                            this,
-                            m_currentSrcString));
+                    if (context()->executionContext()) {
+                        context()->executionContext()->postTask(FROM_HERE,
+                            createCrossThreadTask(&MediaElementAudioSourceHandler::printCORSMessage,
+                                this,
+                                m_currentSrcString));
+                    }
                 }
                 outputBus->zero();
             }
         } else {
             // Either this port doesn't yet support HTMLMediaElement audio stream access,
             // or the stream is not yet available.
             outputBus->zero();
         }
     } else {
         // We failed to acquire the lock.
@@ skipping 56 matching lines @@
 }
 
 void MediaElementAudioSourceNode::unlock()
 {
     mediaElementAudioSourceHandler().unlock();
 }
 
 } // namespace blink
 
 #endif // ENABLE(WEB_AUDIO)