Make File::Duplicate() const

base/files/file_win.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/files/file.h"
 
 #include <io.h>
 #include <stdint.h>
 
 #include "base/logging.h"
@@ skipping 231 matching lines @@
   DCHECK(IsValid());
 
   SCOPED_FILE_TRACE("Unlock");
 
   BOOL result = UnlockFile(file_.Get(), 0, 0, MAXDWORD, MAXDWORD);
   if (!result)
     return OSErrorToFileError(GetLastError());
   return FILE_OK;
 }
 
-File File::Duplicate() {
+File File::Duplicate() const {
   if (!IsValid())
     return File();
 
   SCOPED_FILE_TRACE("Duplicate");
 
   HANDLE other_handle = nullptr;
 
   if (!::DuplicateHandle(GetCurrentProcess(),  // hSourceProcessHandle
                          GetPlatformFile(),
                          GetCurrentProcess(),  // hTargetProcessHandle
@@ skipping 137 matching lines @@
   ThreadRestrictions::AssertIOAllowed();
   DCHECK(IsValid());
   return ::FlushFileBuffers(file_.Get()) != FALSE;
 }
 
 void File::SetPlatformFile(PlatformFile file) {
   file_.Set(file);
 }
 
 }  // namespace base