Make CPDF_Object::GetString() a virtual method.

fpdfsdk/src/formfiller/FFL_CBA_Fontmap.cpp

Index: fpdfsdk/src/formfiller/FFL_CBA_Fontmap.cpp
diff --git a/fpdfsdk/src/formfiller/FFL_CBA_Fontmap.cpp b/fpdfsdk/src/formfiller/FFL_CBA_Fontmap.cpp
index 699a7e4ffeea90cc9847ed712dea12f0192fa33d..6c0742dcc8b82d8a8c84a19cfeb5b6f4c34bd451 100644
--- a/fpdfsdk/src/formfiller/FFL_CBA_Fontmap.cpp
+++ b/fpdfsdk/src/formfiller/FFL_CBA_Fontmap.cpp
@@ -93,7 +93,7 @@ CPDF_Font* CBA_FontMap::FindFontSameCharset(CFX_ByteString& sFontAlias, int32_t
 {
 	ASSERT(m_pAnnotDict != NULL);
 
-	if (m_pAnnotDict->GetString("Subtype") == "Widget")
+	if (m_pAnnotDict->GetStringAt("Subtype") == "Widget")
 	{
 		CPDF_Document* pDocument = GetDocument();
 		ASSERT(pDocument != NULL);
@@ -143,7 +143,8 @@ CPDF_Font* CBA_FontMap::FindResFontSameCharset(CPDF_Dictionary* pResDict, CFX_By
 		if (pDirect == NULL || pDirect->GetType() != PDFOBJ_DICTIONARY) continue;
 
 		CPDF_Dictionary* pElement = (CPDF_Dictionary*)pDirect;
-		if (pElement->GetString("Type") != "Font") continue;
+		if (pElement->GetStringAt("Type") != "Font")
+                    continue;
 
 		CPDF_Font* pFont = pDocument->LoadFont(pElement);
 		if (pFont == NULL) continue;
@@ -230,7 +231,7 @@ CPDF_Font* CBA_FontMap::GetAnnotDefaultFont(CFX_ByteString &sAlias)
 
 	CPDF_Dictionary* pAcroFormDict = NULL;
 
-	FX_BOOL bWidget = (m_pAnnotDict->GetString("Subtype") == "Widget");
+	FX_BOOL bWidget = (m_pAnnotDict->GetStringAt("Subtype") == "Widget");
 
 	if (bWidget)
 	{