Introduce CPDF_Document::FromFPDFDocument().

fpdfsdk/src/fpdfsave.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_edit.h"
 #include "../../public/fpdf_save.h"
 #include "../include/fsdk_define.h"
 
@@ skipping 38 matching lines @@
 
 void CFX_IFileWrite::Release() {
   delete this;
 }
 
 FPDF_BOOL _FPDF_Doc_Save(FPDF_DOCUMENT document,
                          FPDF_FILEWRITE* pFileWrite,
                          FPDF_DWORD flags,
                          FPDF_BOOL bSetVersion,
                          int fileVerion) {
-  CPDF_Document* pDoc = (CPDF_Document*)document;
+  CPDF_Document* pDoc = CPDF_Document::FromFPDFDocument(document);
   if (!pDoc)
     return 0;
 
   if (flags < FPDF_INCREMENTAL || flags > FPDF_REMOVE_SECURITY) {
     flags = 0;
   }
 
   CPDF_Creator FileMaker(pDoc);
   if (bSetVersion)
     FileMaker.SetFileVersion(fileVerion);
@@ skipping 15 matching lines @@
                                             FPDF_DWORD flags) {
   return _FPDF_Doc_Save(document, pFileWrite, flags, FALSE, 0);
 }
 
 DLLEXPORT FPDF_BOOL STDCALL FPDF_SaveWithVersion(FPDF_DOCUMENT document,
                                                  FPDF_FILEWRITE* pFileWrite,
                                                  FPDF_DWORD flags,
                                                  int fileVersion) {
   return _FPDF_Doc_Save(document, pFileWrite, flags, TRUE, fileVersion);
 }