Convert border style defines to an enum class.

core/fpdfdoc/include/fpdf_doc.h

Index: core/fpdfdoc/include/fpdf_doc.h
diff --git a/core/fpdfdoc/include/fpdf_doc.h b/core/fpdfdoc/include/fpdf_doc.h
index d69887bd78b056fcd6786f0315f6a5de4c806c88..8758ab9a423c2b12633212115c9325e6e52f8678 100644
--- a/core/fpdfdoc/include/fpdf_doc.h
+++ b/core/fpdfdoc/include/fpdf_doc.h
@@ -48,6 +48,8 @@ class CPDF_ViewerPreferences;
 class CXML_Element;
 class CFX_RenderDevice;
 
+enum class BorderStyle { SOLID, DASH, BEVELED, INSET, UNDERLINE };
+
 class CPDF_NameTree {
  public:
   explicit CPDF_NameTree(CPDF_Dictionary* pRoot) : m_pRoot(pRoot) {}