Make CPDF_Object::GetString() a virtual method.

core/include/fpdfdoc/fpdf_doc.h

Index: core/include/fpdfdoc/fpdf_doc.h
diff --git a/core/include/fpdfdoc/fpdf_doc.h b/core/include/fpdfdoc/fpdf_doc.h
index fc9d3bce878e61c3682bfd7e4106423d1d394fe6..dfbacee7ab130fa25964b7db94a2698cc8529917 100644
--- a/core/include/fpdfdoc/fpdf_doc.h
+++ b/core/include/fpdfdoc/fpdf_doc.h
@@ -201,25 +201,25 @@ public:
 
     inline CFX_ByteString	GetFileName()
     {
-        return m_pDict->GetString("F");
+        return m_pDict->GetStringAt("F");
     }
 
 
     inline CFX_ByteString	GetDefaultDirectory()
     {
-        return m_pDict->GetString("D");
+        return m_pDict->GetStringAt("D");
     }
 
 
     inline CFX_ByteString	GetOperation()
     {
-        return m_pDict->GetString("O");
+        return m_pDict->GetStringAt("O");
     }
 
 
     inline CFX_ByteString	GetParameter()
     {
-        return m_pDict->GetString("P");
+        return m_pDict->GetStringAt("P");
     }
 
     CPDF_Dictionary*		m_pDict;
@@ -286,7 +286,7 @@ public:
 
     CFX_ByteString		GetTypeName() const
     {
-        return m_pDict->GetString("S");
+        return m_pDict->GetStringAt("S");
     }
 
     ActionType			GetType() const;
@@ -321,7 +321,7 @@ public:
 
     CFX_ByteString		GetNamedAction() const
     {
-        return m_pDict->GetString("N");
+        return m_pDict->GetStringAt("N");
     }
 
     FX_DWORD			GetFlags() const