Fix -Wunused-const-variable warning in Win-Clang build

base/test/test_file_util_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/test/test_file_util.h"
 
 #include <windows.h>
 #include <aclapi.h>
 #include <shlwapi.h>
 
 #include <vector>
 
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/logging.h"
 #include "base/strings/string_split.h"
 #include "base/threading/platform_thread.h"
 #include "base/win/scoped_handle.h"
 
 namespace base {
 
-static const ptrdiff_t kOneMB = 1024 * 1024;
-
 namespace {
 
 struct PermissionInfo {
   PSECURITY_DESCRIPTOR security_descriptor;
   ACL dacl;
 };
 
 // Deny |permission| on the file |path|, for the current user.
 bool DenyFilePermission(const FilePath& path, DWORD permission) {
   PACL old_dacl;
@@ skipping 173 matching lines @@
   DCHECK(info_ != NULL);
   DCHECK_NE(0u, length_);
 }
 
 FilePermissionRestorer::~FilePermissionRestorer() {
   if (!RestorePermissionInfo(path_, info_, length_))
     NOTREACHED();
 }
 
 }  // namespace base