Add type cast definitions for CPDF_Stream.

core/src/fpdfdoc/doc_basic.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 "../../include/fpdfdoc/fpdf_doc.h"
 const int nMaxRecursion = 32;
 int CPDF_Dest::GetPageIndex(CPDF_Document* pDoc) {
   CPDF_Array* pArray = ToArray(m_pObj);
@@ skipping 362 matching lines @@
     result = '/';
     result += ChangeSlashToPDF(filepath.GetPtr());
     return result;
   }
   return ChangeSlashToPDF(filepath.GetPtr());
 #else
   return filepath;
 #endif
 }
 CPDF_Stream* CPDF_FileSpec::GetFileStream() const {
-  if (m_pObj == NULL) {
-    return NULL;
-  }
-  int32_t iType = m_pObj->GetType();
-  if (iType == PDFOBJ_STREAM)
-    return (CPDF_Stream*)m_pObj;
+  if (!m_pObj)
+    return nullptr;
+  if (CPDF_Stream* pStream = m_pObj->AsStream())
+    return pStream;
   if (CPDF_Dictionary* pEF = m_pObj->AsDictionary()->GetDict(FX_BSTRC("EF")))
     return pEF->GetStream(FX_BSTRC("F"));
-  return NULL;
+  return nullptr;
 }
 static void FPDFDOC_FILESPEC_SetFileName(CPDF_Object* pObj,
                                          const CFX_WideStringC& wsFileName,
                                          FX_BOOL bURL) {
   ASSERT(pObj != NULL);
   CFX_WideString wsStr;
   if (bURL) {
     wsStr = wsFileName;
   } else {
     wsStr = FILESPEC_EncodeFileName(wsFileName);
@@ skipping 128 matching lines @@
   int nPage = FXSYS_atoi(bsLbl);
   if (nPage > 0 && nPage <= nPages) {
     return nPage;
   }
   return -1;
 }
 int32_t CPDF_PageLabel::GetPageByLabel(const CFX_WideStringC& wsLabel) const {
   CFX_ByteString bsLabel = PDF_EncodeText(wsLabel.GetPtr());
   return GetPageByLabel(bsLabel);
 }