Add type cast definitions for CPDF_String.

core/src/fpdfdoc/doc_bookmark.cpp

Index: core/src/fpdfdoc/doc_bookmark.cpp
diff --git a/core/src/fpdfdoc/doc_bookmark.cpp b/core/src/fpdfdoc/doc_bookmark.cpp
index 2fea810eccd6b93d2ba1d6e5e42c0400c7ebe6c5..9d2a9f61eada5b2af6a966c419f634161387011a 100644
--- a/core/src/fpdfdoc/doc_bookmark.cpp
+++ b/core/src/fpdfdoc/doc_bookmark.cpp
@@ -51,10 +51,10 @@ CFX_WideString CPDF_Bookmark::GetTitle() const {
   if (!m_pDict) {
     return CFX_WideString();
   }
-  CPDF_String* pString = (CPDF_String*)m_pDict->GetElementValue("Title");
-  if (!pString || pString->GetType() != PDFOBJ_STRING) {
+  CPDF_String* pString = ToString(m_pDict->GetElementValue("Title"));
+  if (!pString)
     return CFX_WideString();
-  }
+
   CFX_WideString title = pString->GetUnicodeText();
   int len = title.GetLength();
   if (!len) {
@@ -75,7 +75,7 @@ CPDF_Dest CPDF_Bookmark::GetDest(CPDF_Document* pDocument) const {
   if (!pDest) {
     return CPDF_Dest();
   }
-  if (pDest->GetType() == PDFOBJ_STRING || pDest->GetType() == PDFOBJ_NAME) {
+  if (pDest->IsString() || pDest->GetType() == PDFOBJ_NAME) {
     CPDF_NameTree name_tree(pDocument, FX_BSTRC("Dests"));
     CFX_ByteStringC name = pDest->GetString();
     return CPDF_Dest(name_tree.LookupNamedDest(pDocument, name));