Make CPDF_Object::GetString() a virtual method.

core/src/fpdfapi/fpdf_edit/fpdf_edit_create.cpp

Index: core/src/fpdfapi/fpdf_edit/fpdf_edit_create.cpp
diff --git a/core/src/fpdfapi/fpdf_edit/fpdf_edit_create.cpp b/core/src/fpdfapi/fpdf_edit/fpdf_edit_create.cpp
index 22826a3609095aa6d194e9be5809966a96406f4a..0b3638437d703093a15a6368e73bfb3718a07dfd 100644
--- a/core/src/fpdfapi/fpdf_edit/fpdf_edit_create.cpp
+++ b/core/src/fpdfapi/fpdf_edit/fpdf_edit_create.cpp
@@ -929,7 +929,7 @@ int32_t CPDF_Creator::WriteIndirectObjectToStream(const CPDF_Object* pObj)
     }
     CPDF_Dictionary *pDict = pObj->GetDict();
     if (pObj->GetType() == PDFOBJ_STREAM) {
-        if (pDict && pDict->GetString(FX_BSTRC("Type")) == FX_BSTRC("XRef")) {
+        if (pDict && pDict->GetStringAt("Type") == "XRef") {
             return 0;
         }
         return 1;
@@ -941,7 +941,7 @@ int32_t CPDF_Creator::WriteIndirectObjectToStream(const CPDF_Object* pObj)
         if (IsSignatureDict(pDict)) {
             return 1;
         }
-        if (pDict->GetString(FX_BSTRC("Type")) == FX_BSTRC("Page")) {
+        if (pDict->GetStringAt("Type") == "Page") {
             return 1;
         }
     }
@@ -2061,7 +2061,7 @@ void CPDF_Creator::InitID(FX_BOOL bDefault )
     }
     m_pIDArray->Add(m_pIDArray->GetElement(0)->Clone());
     if (m_pEncryptDict && !pOldIDArray && m_pParser && bNewId) {
-        if (m_pEncryptDict->GetString(FX_BSTRC("Filter")) == FX_BSTRC("Standard")) {
+        if (m_pEncryptDict->GetStringAt("Filter") == "Standard") {
             CPDF_StandardSecurityHandler handler;
             CFX_ByteString user_pass = m_pParser->GetPassword();
             FX_DWORD flag = PDF_ENCRYPT_CONTENT;