Use std::map as CPDF_Dictionary's underlying store.

fpdfsdk/src/fpdf_flatten.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/fpdf_flatten.h"
 
 #include "fpdfsdk/include/fsdk_define.h"
 
@@ skipping 422 matching lines @@
 
     CPDF_Stream* pAPStream = pAnnotAP->GetStream("N");
     if (!pAPStream) {
       CPDF_Dictionary* pAPDic = pAnnotAP->GetDict("N");
       if (!pAPDic)
         continue;
 
       if (!sAnnotState.IsEmpty()) {
         pAPStream = pAPDic->GetStream(sAnnotState);
       } else {
-        FX_POSITION pos = pAPDic->GetStartPos();
-        if (pos) {
-          CFX_ByteString sKey;
-          CPDF_Object* pFirstObj = pAPDic->GetNextElement(pos, sKey);
+        auto it = pAPDic->begin();
+        if (it != pAPDic->end()) {
+          CPDF_Object* pFirstObj = it->second;
           if (pFirstObj) {
             if (pFirstObj->IsReference())
               pFirstObj = pFirstObj->GetDirect();
             if (!pFirstObj->IsStream())
               continue;
             pAPStream = pFirstObj->AsStream();
           }
         }
       }
     }
@@ skipping 57 matching lines @@
     pNewXObject->SetData((const uint8_t*)sStream, sStream.GetLength(), FALSE,
                          FALSE);
   }
   pPageDict->RemoveAt("Annots");
 
   ObjectArray.RemoveAll();
   RectArray.RemoveAll();
 
   return FLATTEN_SUCCESS;
 }