Add test for StringToCode and StringToWideString.

core/src/fpdfapi/fpdf_font/font_int.h

Index: core/src/fpdfapi/fpdf_font/font_int.h
diff --git a/core/src/fpdfapi/fpdf_font/font_int.h b/core/src/fpdfapi/fpdf_font/font_int.h
index 48e58d6345279040634338ed063fb976acd50ebc..559027b283e1d0c1f106076ea8be0cca2c3c7a98 100644
--- a/core/src/fpdfapi/fpdf_font/font_int.h
+++ b/core/src/fpdfapi/fpdf_font/font_int.h
@@ -174,6 +174,13 @@ class CPDF_ToUnicodeMap {
   std::map<FX_DWORD, FX_DWORD> m_Map;
   CPDF_CID2UnicodeMap* m_pBaseMap;
   CFX_WideTextBuf m_MultiCharBuf;
+
+ private:
+  friend class fpdf_font_StringToCode_Test;
+  friend class fpdf_font_StringToWideString_Test;
+
+  static FX_DWORD StringToCode(const CFX_ByteStringC& str);
+  static CFX_WideString StringToWideString(const CFX_ByteStringC& str);
 };
 class CPDF_FontCharMap : public CFX_CharMap {
  public: