Make CPDF_Object::GetString() a virtual method.

core/src/fpdfapi/fpdf_parser/fpdf_parser_fdf.cpp

Index: core/src/fpdfapi/fpdf_parser/fpdf_parser_fdf.cpp
diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_fdf.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_fdf.cpp
index 0471250fd958c309477af1713daa4e33e2d23323..83eaf72573de533a24ae9f096438529a28280626 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_fdf.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_fdf.cpp
@@ -158,13 +158,13 @@ CFX_WideString	FPDF_FileSpec_GetWin32Path(const CPDF_Object* pFileSpec)
         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)