Validate execution context before printing CORS 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 123 matching lines @@
 }
 
 bool MediaElementAudioSourceHandler::passesCurrentSrcCORSAccessCheck(const KURL& currentSrc)
 {
     ASSERT(isMainThread());
     return context()->securityOrigin() && context()->securityOrigin()->canRequest(currentSrc);
 }
 
 void MediaElementAudioSourceHandler::printCORSMessage(const String& message)
 {
-    context()->executionContext()->addConsoleMessage(
-        ConsoleMessage::create(SecurityMessageSource, InfoMessageLevel,
-            "MediaElementAudioSource outputs zeroes due to CORS access restrictions for " + message));
+    if (context()->executionContext()) {

[hongchan, 2015/06/16 16:12:10]

What happens if executionContext() does not exist? Is it even possible? (Perhaps
the context from a closed tab?)

+        context()->executionContext()->addConsoleMessage(
+            ConsoleMessage::create(SecurityMessageSource, InfoMessageLevel,
+                "MediaElementAudioSource outputs zeroes due to CORS access restrictions for " + message));
+    }
 }
 
 void MediaElementAudioSourceHandler::process(size_t numberOfFrames)
 {
     AudioBus* outputBus = output(0).bus();
 
     if (!mediaElement() || !m_sourceNumberOfChannels || !m_sourceSampleRate) {
         outputBus->zero();
         return;
     }
@@ skipping 93 matching lines @@
 }
 
 void MediaElementAudioSourceNode::unlock()
 {
     mediaElementAudioSourceHandler().unlock();
 }
 
 } // namespace blink
 
 #endif // ENABLE(WEB_AUDIO)