Onerror return value handling in workers fixed as per HTML5 spec.

Source/core/workers/WorkerMessagingProxy.cpp

 /*
  * Copyright (C) 2008 Apple Inc. All Rights Reserved.
  * Copyright (C) 2009 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
@@ skipping 156 matching lines @@
 
 void WorkerMessagingProxy::reportException(const String& errorMessage, int lineNumber, int columnNumber, const String& sourceURL)
 {
     if (!m_workerObject)
         return;
 
     // We don't bother checking the askedToTerminate() flag here, because exceptions should *always* be reported even if the thread is terminated.
     // This is intentionally different than the behavior in MessageWorkerTask, because terminated workers no longer deliver messages (section 4.6 of the WebWorker spec), but they do report exceptions.
 
     RefPtrWillBeRawPtr<ErrorEvent> event = ErrorEvent::create(errorMessage, sourceURL, lineNumber, columnNumber, 0);
-    bool errorHandled = !m_workerObject->dispatchEvent(event);
+    // Pass it on the error if "false" is returned, if "true" don't.
+    bool errorHandled = m_workerObject->dispatchEvent(event);
     if (!errorHandled)
         m_executionContext->reportException(event, 0, nullptr, NotSharableCrossOrigin);
 }
 
 void WorkerMessagingProxy::reportConsoleMessage(MessageSource source, MessageLevel level, const String& message, int lineNumber, const String& sourceURL)
 {
     if (m_askedToTerminate)
         return;
     // FIXME: In case of nested workers, this should go directly to the root Document context.
     ASSERT(m_executionContext->isDocument());
@@ skipping 99 matching lines @@
 
     // FIXME: This need to be revisited when we support nested worker one day
     ASSERT(m_executionContext->isDocument());
     Document* document = toDocument(m_executionContext.get());
     LocalFrame* frame = document->frame();
     if (frame)
         frame->console().adoptWorkerMessagesAfterTermination(this);
 }
 
 } // namespace blink