Convert XFA_ELEMENT to an enum class

xfa/fxfa/parser/cxfa_caption.cpp

Index: xfa/fxfa/parser/cxfa_caption.cpp
diff --git a/xfa/fxfa/parser/cxfa_caption.cpp b/xfa/fxfa/parser/cxfa_caption.cpp
index 1d343e7e43249336b954219b3ec1516e88a0a1e3..6606d513966e3e1c679027f2cb8945c21a555e4a 100644
--- a/xfa/fxfa/parser/cxfa_caption.cpp
+++ b/xfa/fxfa/parser/cxfa_caption.cpp
@@ -29,13 +29,15 @@ FX_FLOAT CXFA_Caption::GetReserve() {
 }
 
 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);
 }