Fix abort above FPDFPage_Flatten

fpdfsdk/cpdfsdk_formfillenvironment.h

 // Copyright 2016 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
 
 #ifndef FPDFSDK_CPDFSDK_FORMFILLENVIRONMENT_H_
 #define FPDFSDK_CPDFSDK_FORMFILLENVIRONMENT_H_
 
 #include <memory>
@@ skipping 195 matching lines @@
   CPDFSDK_AnnotHandlerMgr* GetAnnotHandlerMgr();  // Creates if not present.
   IJS_Runtime* GetJSRuntime();                    // Creates if not present.
   CPDFSDK_ActionHandler* GetActionHander();       // Creates if not present.
   CPDFSDK_InterForm* GetInterForm();              // Creates if not present.
 
  private:
   std::unique_ptr<CPDFSDK_AnnotHandlerMgr> m_pAnnotHandlerMgr;
   std::unique_ptr<CPDFSDK_ActionHandler> m_pActionHandler;
   std::unique_ptr<IJS_Runtime> m_pJSRuntime;
   FPDF_FORMFILLINFO* const m_pInfo;
-  std::map<UnderlyingPageType*, std::unique_ptr<CPDFSDK_PageView>> m_pageMap;
   std::unique_ptr<CPDFSDK_InterForm> m_pInterForm;
   CPDFSDK_Annot::ObservedPtr m_pFocusAnnot;
   UnderlyingDocumentType* m_pUnderlyingDoc;
   std::unique_ptr<CFFL_InteractiveFormFiller> m_pFormFiller;
   std::unique_ptr<CFX_SystemHandler> m_pSysHandler;
   bool m_bChangeMask;
   bool m_bBeingDestroyed;
+
+  // Must be destroyed first.
+  std::map<UnderlyingPageType*, std::unique_ptr<CPDFSDK_PageView>> m_pageMap;
 };
 
 #endif  // FPDFSDK_CPDFSDK_FORMFILLENVIRONMENT_H_