Fix a potential UAF with FPDFAvail_IsLinearized().

core/fpdfapi/fpdf_parser/cpdf_hint_tables.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 CORE_FPDFAPI_FPDF_PARSER_CPDF_HINT_TABLES_H_
 #define CORE_FPDFAPI_FPDF_PARSER_CPDF_HINT_TABLES_H_
 
 #include <vector>
 
 #include "core/fpdfapi/fpdf_parser/include/ipdf_data_avail.h"
 #include "core/fxcrt/include/fx_basic.h"
 #include "core/fxcrt/include/fx_stream.h"
 
 class CFX_BitStream;
 class CPDF_DataAvail;
 class CPDF_Dictionary;
 class CPDF_Stream;
 
 class CPDF_HintTables {
  public:
   CPDF_HintTables(CPDF_DataAvail* pDataAvail, CPDF_Dictionary* pLinearized)
-      : m_pLinearizedDict(pLinearized),
-        m_pDataAvail(pDataAvail),
+      : m_pDataAvail(pDataAvail),
+        m_pLinearizedDict(pLinearized),
         m_nFirstPageSharedObjs(0),
         m_szFirstPageObjOffset(0) {}
   ~CPDF_HintTables();
 
   FX_BOOL GetPagePos(int index,
                      FX_FILESIZE& szPageStartPos,
                      FX_FILESIZE& szPageLength,
                      uint32_t& dwObjNum);
 
   IPDF_DataAvail::DocAvailStatus CheckPage(
       int index,
       IPDF_DataAvail::DownloadHints* pHints);
 
   FX_BOOL LoadHintStream(CPDF_Stream* pHintStream);
 
  protected:
   FX_BOOL ReadPageHintTable(CFX_BitStream* hStream);
   FX_BOOL ReadSharedObjHintTable(CFX_BitStream* hStream, uint32_t offset);
   uint32_t GetItemLength(int index, const std::vector<FX_FILESIZE>& szArray);
 
  private:
   int ReadPrimaryHintStreamOffset() const;
   int ReadPrimaryHintStreamLength() const;
 
-  CPDF_Dictionary* m_pLinearizedDict;
-  CPDF_DataAvail* m_pDataAvail;
+  // Owner, outlives this object.
+  CPDF_DataAvail* const m_pDataAvail;
+
+  // Owned by |m_pDataAvail|.
+  CPDF_Dictionary* const m_pLinearizedDict;
+
   uint32_t m_nFirstPageSharedObjs;
   FX_FILESIZE m_szFirstPageObjOffset;
   CFX_ArrayTemplate<uint32_t> m_dwDeltaNObjsArray;
   CFX_ArrayTemplate<uint32_t> m_dwNSharedObjsArray;
   CFX_ArrayTemplate<uint32_t> m_dwSharedObjNumArray;
   CFX_ArrayTemplate<uint32_t> m_dwIdentifierArray;
   std::vector<FX_FILESIZE> m_szPageOffsetArray;
   std::vector<FX_FILESIZE> m_szSharedObjOffsetArray;
 };
 
 #endif  // CORE_FPDFAPI_FPDF_PARSER_CPDF_HINT_TABLES_H_