Subject .mm files to the header sorting presubmit

sync/util/get_session_name_mac.mm

 // 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 "sync/util/get_session_name_mac.h"
 
+#include <sys/sysctl.h>
 #import <SystemConfiguration/SCDynamicStoreCopySpecific.h>
-#include <sys/sysctl.h>
 
 #include "base/mac/scoped_cftyperef.h"
 #include "base/strings/string_util.h"
 #include "base/strings/sys_string_conversions.h"
 
 namespace syncer {
 namespace internal {
 
 std::string GetHardwareModelName() {
   // Do not use NSHost currentHost, as it's very slow. http://crbug.com/138570
@@ skipping 20 matching lines @@
       if (IsAsciiDigit(modelBuffer[i]))
         return std::string(modelBuffer, 0, i);
     }
     return std::string(modelBuffer, 0, length);
   }
   return "Unknown";
 }
 
 }  // namespace internal
 }  // namespace syncer