Add type cast definitions for CPDF_String.

core/src/fpdfapi/fpdf_parser/fpdf_parser_utility.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 "../../../include/fpdfapi/fpdf_parser.h"
 const char PDF_CharType[256] = {
     // NUL  SOH  STX  ETX  EOT  ENQ  ACK  BEL  BS   HT   LF   VT   FF   CR   SO
     // SI
@@ skipping 356 matching lines @@
   switch (pObj->GetType()) {
     case PDFOBJ_NULL:
       buf << FX_BSTRC(" null");
       break;
     case PDFOBJ_BOOLEAN:
     case PDFOBJ_NUMBER:
       buf << " " << pObj->GetString();
       break;
     case PDFOBJ_STRING: {
       CFX_ByteString str = pObj->GetString();
-      FX_BOOL bHex = ((CPDF_String*)pObj)->IsHex();
+      FX_BOOL bHex = pObj->AsString()->IsHex();
       buf << PDF_EncodeString(str, bHex);
       break;
     }
     case PDFOBJ_NAME: {
       CFX_ByteString str = pObj->GetString();
       buf << FX_BSTRC("/") << PDF_NameEncode(str);
       break;
     }
     case PDFOBJ_REFERENCE: {
       CPDF_Reference* p = (CPDF_Reference*)pObj;
@@ skipping 87 matching lines @@
     CPDF_Object* pFound = SearchNumberNode(pKid, num);
     if (pFound) {
       return pFound;
     }
   }
   return NULL;
 }
 CPDF_Object* CPDF_NumberTree::LookupValue(int num) {
   return SearchNumberNode(m_pRoot, num);
 }