Remove StyleEngine.h include from RenderObject.h

Source/core/css/DragUpdateTest.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/dom/Element.h"
+#include "core/dom/StyleEngine.h"
 #include "core/frame/FrameView.h"
 #include "core/html/HTMLDocument.h"
 #include "core/html/HTMLElement.h"
 #include "core/testing/DummyPageHolder.h"
 #include <gtest/gtest.h>
 
 using namespace WebCore;
 
 namespace {
 
@@ skipping 43 matching lines @@
 
     document->documentElement()->renderer()->updateDragState(true);
     document->updateLayout();
 
     unsigned accessCount = document->styleEngine()->resolverAccessCount() - startCount;
 
     ASSERT_EQ(5U, accessCount);
 }
 
 } // namespace