Add APIs for limited use of document tagged code.

fpdfsdk/fpdfview.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "public/fpdfview.h"
 
 #include <memory>
 #include <utility>
@@ skipping 1092 matching lines @@
       return nullptr;
   }
   if (!pDestObj->IsArray())
     return nullptr;
 
   CFX_WideString wsName = PDF_DecodeText(bsName);
   CFX_ByteString utf16Name = wsName.UTF16LE_Encode();
   int len = utf16Name.GetLength();
   if (!buffer) {
     *buflen = len;
-  } else if (*buflen >= len) {
+  } else if (len <= *buflen) {
     memcpy(buffer, utf16Name.c_str(), len);
     *buflen = len;
   } else {
     *buflen = -1;
   }
   return (FPDF_DEST)pDestObj;
 }