Make down-conversion explicit from CFX_ByteString to CFX_ByteStringC.

core/fpdfdoc/doc_formfield.cpp

 // Copyright 2014 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 "core/fpdfapi/fpdf_parser/include/cfdf_document.h"
 #include "core/fpdfapi/fpdf_parser/include/cpdf_array.h"
 #include "core/fpdfapi/fpdf_parser/include/cpdf_document.h"
 #include "core/fpdfapi/fpdf_parser/include/cpdf_number.h"
@@ skipping 1036 matching lines @@
   CFX_ByteString DA;
   if (CPDF_Object* pObj_t = FPDF_GetFieldAttr(m_pDict, "DA")) {
     DA = pObj_t->GetString();
   }
   if (DA.IsEmpty() && m_pForm->m_pFormDict) {
     DA = m_pForm->m_pFormDict->GetStringBy("DA");
   }
   if (DA.IsEmpty()) {
     return;
   }
-  CPDF_SimpleParser syntax(DA);
+  CPDF_SimpleParser syntax(DA.AsByteStringC());
   syntax.FindTagParamFromStart("Tf", 2);
   CFX_ByteString font_name = syntax.GetWord();
   CPDF_Dictionary* pFontDict = NULL;
   if (m_pForm->m_pFormDict && m_pForm->m_pFormDict->GetDictBy("DR") &&
       m_pForm->m_pFormDict->GetDictBy("DR")->GetDictBy("Font"))
     pFontDict = m_pForm->m_pFormDict->GetDictBy("DR")
                     ->GetDictBy("Font")
-                    ->GetDictBy(font_name);
+                    ->GetDictBy(font_name.AsByteStringC());
 
   if (!pFontDict) {
     return;
   }
   m_pFont = m_pForm->m_pDocument->LoadFont(pFontDict);
   m_FontSize = FX_atof(syntax.GetWord());
 }