Subject .mm files to the header sorting presubmit

chrome/browser/ui/cocoa/bubble_combobox.mm

 // Copyright 2014 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.
 
 #import "chrome/browser/ui/cocoa/bubble_combobox.h"
 
+#include "base/strings/sys_string_conversions.h"
 #include "ui/base/models/combobox_model.h"
-#include "base/strings/sys_string_conversions.h"
 
 @implementation BubbleCombobox
 
 - (id)initWithFrame:(NSRect)frame
           pullsDown:(BOOL)pullsDown
               model:(ui::ComboboxModel*)model {
   if ((self = [super initWithFrame:frame pullsDown:pullsDown])) {
     [self setFont:[NSFont systemFontOfSize:[NSFont smallSystemFontSize]]];
     [self setBordered:YES];
     [[self cell] setControlSize:NSSmallControlSize];
 
     for (int i = 0; i < model->GetItemCount(); ++i) {
       if (model->IsItemSeparatorAt(i))
         [[self menu] addItem:[NSMenuItem separatorItem]];
       else
         [self addItemWithTitle:base::SysUTF16ToNSString(model->GetItemAt(i))];
     }
 
     [self selectItemAtIndex:model->GetDefaultIndex()];
   }
   return self;
 }
 
 @end