Assert that dictionary can own the objects it is given.

core/fpdfapi/fpdf_parser/cpdf_dictionary.cpp

 // 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
 
 #include "core/fpdfapi/fpdf_parser/include/cpdf_dictionary.h"
 
 #include <set>
 #include <utility>
@@ skipping 151 matching lines @@
 }
 
 bool CPDF_Dictionary::IsSignatureDict() const {
   CPDF_Object* pType = GetDirectObjectFor("Type");
   if (!pType)
     pType = GetDirectObjectFor("FT");
   return pType && pType->GetString() == "Sig";
 }
 
 void CPDF_Dictionary::SetFor(const CFX_ByteString& key, CPDF_Object* pObj) {
+  ASSERT(!pObj || pObj->GetObjNum() == 0);
   auto it = m_Map.find(key);
   if (it == m_Map.end()) {
     if (pObj)
       m_Map.insert(std::make_pair(key, pObj));
     return;
   }
 
   if (it->second == pObj)
     return;
   it->second->Release();
@@ skipping 74 matching lines @@
                                    const CFX_Matrix& matrix) {
   CPDF_Array* pArray = new CPDF_Array;
   pArray->AddNumber(matrix.a);
   pArray->AddNumber(matrix.b);
   pArray->AddNumber(matrix.c);
   pArray->AddNumber(matrix.d);
   pArray->AddNumber(matrix.e);
   pArray->AddNumber(matrix.f);
   SetFor(key, pArray);
 }