Convert XFA_ELEMENT to an enum class

xfa/fxfa/parser/cxfa_caption.cpp

 // Copyright 2016 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "xfa/fxfa/parser/cxfa_caption.h"
 
 #include "xfa/fxfa/parser/xfa_object.h"
 
@@ skipping 11 matching lines @@
   return eAttr;
 }
 
 FX_FLOAT CXFA_Caption::GetReserve() {
   CXFA_Measurement ms;
   m_pNode->TryMeasure(XFA_ATTRIBUTE_Reserve, ms);
   return ms.ToUnit(XFA_UNIT_Pt);
 }
 
 CXFA_Margin CXFA_Caption::GetMargin() {
-  return CXFA_Margin(m_pNode ? m_pNode->GetChild(0, XFA_ELEMENT_Margin) : NULL);
+  return CXFA_Margin(m_pNode ? m_pNode->GetChild(0, XFA_Element::Margin)
+                             : nullptr);
 }
 
 CXFA_Font CXFA_Caption::GetFont() {
-  return CXFA_Font(m_pNode ? m_pNode->GetChild(0, XFA_ELEMENT_Font) : NULL);
+  return CXFA_Font(m_pNode ? m_pNode->GetChild(0, XFA_Element::Font) : nullptr);
 }
 
 CXFA_Value CXFA_Caption::GetValue() {
-  return CXFA_Value(m_pNode ? m_pNode->GetChild(0, XFA_ELEMENT_Value) : NULL);
+  return CXFA_Value(m_pNode ? m_pNode->GetChild(0, XFA_Element::Value)
+                            : nullptr);
 }