Include Event.h in fewer header files

Source/core/testing/NullExecutionContext.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
+#include "core/testing/NullExecutionContext.h"
 
-#include "core/testing/NullExecutionContext.h"
+#include "core/events/Event.h"
 
 namespace WebCore {
 
 namespace {
 
 class NullEventQueue FINAL : public EventQueue {
 public:
     NullEventQueue() { }
     virtual ~NullEventQueue() { }
     virtual bool enqueueEvent(PassRefPtrWillBeRawPtr<Event>) OVERRIDE { return true; }
     virtual bool cancelEvent(Event*) OVERRIDE { return true; }
     virtual void close() OVERRIDE { }
 };
 
 } // namespace
 
 NullExecutionContext::NullExecutionContext()
     : m_tasksNeedSuspension(false)
     , m_queue(adoptPtrWillBeNoop(new NullEventQueue()))
 {
 }
 
 } // namespace WebCore