Fix non-Oilpan build following r375261.

third_party/WebKit/Source/core/input/PointerEventManager.cpp

 // Copyright 2015 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 "core/input/PointerEventManager.h"
 
 #include "core/dom/shadow/FlatTreeTraversal.h"
 #include "core/events/MouseEvent.h"
 #include "core/input/EventHandler.h"
 
@@ skipping 340 matching lines @@
     unsigned modifiers)
 {
 
     if (MouseEvent::platformModifiersToButtons(modifiers) ==
         static_cast<unsigned short>(MouseEvent::Buttons::None))
         m_preventMouseEventForPointerTypeMouse = false;
 }
 
 DEFINE_TRACE(PointerEventManager)
 {
+#if ENABLE(OILPAN)
     visitor->trace(m_nodeUnderPointer);
+#endif
 }
 
 
 } // namespace blink