Make CPDF_Object::GetString() a virtual method.

core/src/fpdfapi/fpdf_parser/fpdf_parser_fdf.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_serial.h"
 CFDF_Document::CFDF_Document() : CPDF_IndirectObjects(NULL)
 {
     m_pRootDict = NULL;
@@ skipping 140 matching lines @@
         ((CPDF_Dictionary*)pFileSpec)->RemoveAt(FX_BSTRC("FS"));
     }
 }
 CFX_WideString  FPDF_FileSpec_GetWin32Path(const CPDF_Object* pFileSpec)
 {
     CFX_WideString wsFileName;
     if (pFileSpec->GetType() == PDFOBJ_DICTIONARY) {
         CPDF_Dictionary* pDict = (CPDF_Dictionary*)pFileSpec;
         wsFileName = pDict->GetUnicodeText(FX_BSTRC("UF"));
         if (wsFileName.IsEmpty()) {
-            wsFileName = CFX_WideString::FromLocal(pDict->GetString(FX_BSTRC("F")));
+            wsFileName = CFX_WideString::FromLocal(pDict->GetStringAt("F"));
         }
-        if (pDict->GetString(FX_BSTRC("FS")) == FX_BSTRC("URL")) {
+        if (pDict->GetStringAt("FS") == "URL") {
             return wsFileName;
         }
         if (wsFileName.IsEmpty() && pDict->KeyExist(FX_BSTRC("DOS"))) {
-            wsFileName = CFX_WideString::FromLocal(pDict->GetString(FX_BSTRC("DOS")));
+            wsFileName = CFX_WideString::FromLocal(pDict->GetStringAt("DOS"));
         }
     }
     else if (!pFileSpec)
         wsFileName = CFX_WideString();
     else {
         wsFileName = CFX_WideString::FromLocal(pFileSpec->GetString());
     }
     if (wsFileName[0] != '/') {
         return ChangeSlash(wsFileName.c_str());
     }
     if (wsFileName[2] == '/') {
         CFX_WideString result;
         result += wsFileName[1];
         result += ':';
         result += ChangeSlash(wsFileName.c_str() + 2);
         return result;
     } else {
         CFX_WideString result;
         result += '\\';
         result += ChangeSlash(wsFileName.c_str());
         return result;
     }
 }