Rework dispatchEvent so it is consistent for isTrusted support.

Source/core/workers/WorkerEventQueue.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 54 matching lines @@
     {
         return adoptPtr(new EventDispatcherTask(event, eventQueue));
     }
 
     ~EventDispatcherTask() override
     {
         if (m_event)
             m_eventQueue->removeEvent(m_event.get());
     }
 
-    void dispatchEvent(ExecutionContext*, PassRefPtrWillBeRawPtr<Event> event)
+    void dispatchEvent(ExecutionContext*, PassRefPtrWillBeRawPtr<Event> prpEvent)
     {
+        // Stash the event on the stack in a RefPtrWillBeRawPtr; trying to do this
+        // in a single line causes an optimization bug with MSVC. MSVC generates code
+        // that passes the event arg (forcing PassRefPtrWillBeRawPtr to be released)
+        // before the target is queried.

[tkent, 2015/07/16 00:22:03]

Wow, nice detective work.

+        RefPtrWillBeRawPtr<Event> event = prpEvent;
         event->target()->dispatchEvent(event);
     }
 
     virtual void performTask(ExecutionContext* context)
     {
         if (m_isCancelled)
             return;
         m_eventQueue->removeEvent(m_event.get());
         dispatchEvent(context, m_event);
         m_event.clear();
@@ skipping 52 matching lines @@
     for (const auto& entry : m_eventTaskMap) {
         Event* event = entry.key.get();
         EventDispatcherTask* task = entry.value;
         InspectorInstrumentation::didRemoveEvent(event->target(), event);
         task->cancel();
     }
     m_eventTaskMap.clear();
 }
 
 }