Convert loose FX_Create* functions into static methods

xfa/fxfa/app/xfa_ffdoc.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 "xfa/fxfa/xfa_ffdoc.h"
 
 #include <algorithm>
 #include <memory>
@@ skipping 399 matching lines @@
     }
   }
 
   CPDF_Stream* pStream = ToStream(pObject);
   if (!pStream)
     return nullptr;
 
   CPDF_StreamAcc streamAcc;
   streamAcc.LoadAllData(pStream);
 
-  IFX_SeekableReadStream* pImageFileRead =
-      FX_CreateMemoryStream((uint8_t*)streamAcc.GetData(), streamAcc.GetSize());
+  IFX_SeekableReadStream* pImageFileRead = IFX_MemoryStream::Create(
+      (uint8_t*)streamAcc.GetData(), streamAcc.GetSize());
 
   CFX_DIBitmap* pDibSource = XFA_LoadImageFromBuffer(
       pImageFileRead, FXCODEC_IMAGE_UNKNOWN, iImageXDpi, iImageYDpi);
   m_HashToDibDpiMap[dwHash] = {pDibSource, iImageXDpi, iImageYDpi};
   pImageFileRead->Release();
   return pDibSource;
 }
 
 bool CXFA_FFDoc::SavePackage(XFA_HashCode code,
                              IFX_SeekableWriteStream* pFile,
@@ skipping 12 matching lines @@
 
   return !!pExport->Export(
       pFile, pNode, 0, bsChecksum.GetLength() ? bsChecksum.c_str() : nullptr);
 }
 
 bool CXFA_FFDoc::ImportData(IFX_SeekableReadStream* pStream, bool bXDP) {
   std::unique_ptr<CXFA_DataImporter> importer(
       new CXFA_DataImporter(m_pDocumentParser->GetDocument()));
   return importer->ImportData(pStream);
 }