Make CPDF_Object::GetString() a virtual method.

core/src/fpdfdoc/doc_form.cpp

Index: core/src/fpdfdoc/doc_form.cpp
diff --git a/core/src/fpdfdoc/doc_form.cpp b/core/src/fpdfdoc/doc_form.cpp
index 2b59bee6ee6f8aedd85fe4370af18e0d37f77984..35ffd4bf4aaedae5a73eed14820f0629d33867e4 100644
--- a/core/src/fpdfdoc/doc_form.cpp
+++ b/core/src/fpdfdoc/doc_form.cpp
@@ -1131,7 +1131,7 @@ CPDF_DefaultAppearance CPDF_InterForm::GetDefaultAppearance()
     if (m_pFormDict == NULL) {
         return csDA;
     }
-    csDA = m_pFormDict->GetString("DA");
+    csDA = m_pFormDict->GetStringAt("DA");
     return csDA;
 }
 CPDF_Font* CPDF_InterForm::GetDefaultFormFont()
@@ -1274,7 +1274,7 @@ void CPDF_InterForm::FixPageFields(const CPDF_Page* pPage)
     int iAnnotCount = pAnnots->GetCount();
     for (int i = 0; i < iAnnotCount; i++) {
         CPDF_Dictionary* pAnnot = pAnnots->GetDict(i);
-        if (pAnnot != NULL && pAnnot->GetString(FX_BSTRC("Subtype")) == "Widget") {
+        if (pAnnot && pAnnot->GetStringAt("Subtype") == "Widget") {
             LoadField(pAnnot);
         }
     }
@@ -1294,7 +1294,7 @@ CPDF_FormField* CPDF_InterForm::AddTerminalField(const CPDF_Dictionary* pFieldDi
     if (pField == NULL) {
         CPDF_Dictionary *pParent = (CPDF_Dictionary*)pFieldDict;
         if (!pFieldDict->KeyExist(FX_BSTRC("T")) &&
-            pFieldDict->GetString(FX_BSTRC("Subtype")) == FX_BSTRC("Widget")) {
+            pFieldDict->GetStringAt("Subtype") == "Widget") {
             pParent = pFieldDict->GetDict(FX_BSTRC("Parent"));
             if (!pParent) {
                 pParent = (CPDF_Dictionary*)pFieldDict;
@@ -1328,7 +1328,7 @@ CPDF_FormField* CPDF_InterForm::AddTerminalField(const CPDF_Dictionary* pFieldDi
     }
     CPDF_Array* pKids = pFieldDict->GetArray("Kids");
     if (pKids == NULL) {
-        if (pFieldDict->GetString("Subtype") == "Widget") {
+        if (pFieldDict->GetStringAt("Subtype") == "Widget") {
             AddControl(pField, pFieldDict);
         }
     } else {
@@ -1337,7 +1337,7 @@ CPDF_FormField* CPDF_InterForm::AddTerminalField(const CPDF_Dictionary* pFieldDi
             if (pKid == NULL) {
                 continue;
             }
-            if (pKid->GetString("Subtype") != "Widget") {
+            if (pKid->GetStringAt("Subtype") != "Widget") {
                 continue;
             }
             AddControl(pField, pKid);
@@ -1378,7 +1378,8 @@ CPDF_FormField* CPDF_InterForm::CheckRequiredFields(const CFX_PtrArray *fields,
         }
         if ((bIncludeOrExclude && bFind) || (!bIncludeOrExclude && !bFind)) {
             CPDF_Dictionary *pFieldDict = pField->m_pDict;
-            if ((dwFlags & 0x02) != 0 && pFieldDict->GetString("V").IsEmpty()) {
+            if ((dwFlags & 0x02) != 0 &&
+                pFieldDict->GetStringAt("V").IsEmpty()) {
                 return pField;
             }
         }
@@ -1431,7 +1432,8 @@ CFDF_Document* CPDF_InterForm::ExportToFDF(const CFX_WideStringC& pdf_path, CFX_
         }
         FX_BOOL bFind = fields.Find(pField, 0) >= 0;
         if ((bIncludeOrExclude && bFind) || (!bIncludeOrExclude && !bFind)) {
-            if ((dwFlags & 0x02) != 0 && pField->m_pDict->GetString("V").IsEmpty()) {
+            if ((dwFlags & 0x02) != 0 &&
+                pField->m_pDict->GetStringAt("V").IsEmpty()) {
                 continue;
             }
             CFX_WideString fullname = GetFullName(pField->GetFieldDict());
@@ -1477,7 +1479,7 @@ const struct _SupportFieldEncoding {
 static void FPDFDOC_FDF_GetFieldValue(CPDF_Dictionary *pFieldDict, CFX_WideString &csValue, CFX_ByteString &bsEncoding)
 {
     ASSERT(pFieldDict != NULL);
-    CFX_ByteString csBValue = pFieldDict->GetString("V");
+    CFX_ByteString csBValue = pFieldDict->GetStringAt("V");
     int32_t iCount = sizeof(g_fieldEncoding) / sizeof(g_fieldEncoding[0]);
     int32_t i = 0;
     for (; i < iCount; ++i)
@@ -1573,7 +1575,7 @@ FX_BOOL CPDF_InterForm::ImportFromFDF(const CFDF_Document* pFDF, FX_BOOL bNotify
     if (pFields == NULL) {
         return FALSE;
     }
-    m_bsEncoding = pMainDict->GetString(FX_BSTRC("Encoding"));
+    m_bsEncoding = pMainDict->GetStringAt("Encoding");
     if (bNotify && m_pFormNotify != NULL) {
         int iRet = m_pFormNotify->BeforeFormImportData(this);
         if (iRet < 0) {