Make CFX_WideString(const CFX_WideString&) explicit.

xfa/fgas/localization/fgas_localemgr.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/fgas/localization/fgas_localemgr.h"
 
 #include "core/fxcrt/include/fx_xml.h"
 
@@ skipping 73 matching lines @@
   if (!pLocale) {
     CXML_Element* pxml =
         (CXML_Element*)m_lcid2xml.GetValueAt((void*)(uintptr_t)lcid);
     if (pxml) {
       pLocale = IFX_Locale::Create(pxml);
       m_lcid2locale.SetAt((void*)(uintptr_t)lcid, pLocale);
     }
   }
   return pLocale;
 }
-IFX_Locale* CFX_LocaleMgr::GetLocaleByName(
-    const CFX_WideStringC& wsLocaleName) {
-  return NULL;
+IFX_Locale* CFX_LocaleMgr::GetLocaleByName(const CFX_WideString& wsLocaleName) {
+  return nullptr;
 }