Avoid two C-style FX_WCHAR* casts in pdfium

xfa/fde/css/fde_csssyntax.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/fde/css/fde_csssyntax.h"
 
 #include "xfa/fde/css/fde_cssdatatable.h"
 #include "xfa/fgas/crt/fgas_codepage.h"
@@ skipping 408 matching lines @@
 void CFDE_CSSTextBuf::Reset() {
   if (!m_bExtBuf) {
     FX_Free(m_pBuffer);
     m_pBuffer = NULL;
   }
   m_iDatPos = m_iDatLen = m_iBufLen;
 }
 FX_BOOL CFDE_CSSTextBuf::AttachBuffer(const FX_WCHAR* pBuffer,
                                       int32_t iBufLen) {
   Reset();
-  m_pBuffer = (FX_WCHAR*)pBuffer;
+  m_pBuffer = const_cast<FX_WCHAR*>(pBuffer);
   m_iDatLen = m_iBufLen = iBufLen;
   return m_bExtBuf = TRUE;
 }
 FX_BOOL CFDE_CSSTextBuf::EstimateSize(int32_t iAllocSize) {
   ASSERT(iAllocSize > 0);
   Clear();
   m_bExtBuf = FALSE;
   return ExpandBuf(iAllocSize);
 }
 int32_t CFDE_CSSTextBuf::LoadFromStream(IFX_Stream* pTxtStream,
@@ skipping 35 matching lines @@
   if (iLength > m_iDatLen - iStart) {
     iLength = m_iDatLen - iStart;
   }
   if (iLength < 0) {
     iLength = 0;
   } else {
     FXSYS_memmove(m_pBuffer, m_pBuffer + iStart, iLength * sizeof(FX_WCHAR));
   }
   m_iDatLen = iLength;
 }