MD Settings: Simplify settings-dropdown-menu

chrome/browser/resources/settings/prefs/compiled_resources.gyp

 # Copyright 2015 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.
 {
   'targets': [
     {
       'target_name': 'prefs',
       'variables': {
         'depends': [
           '../../../../../ui/webui/resources/js/compiled_resources.gyp:assert',
           '../../../../../ui/webui/resources/js/compiled_resources.gyp:cr',
           'prefs_behavior.js',
           'prefs_types.js',
+          'selectable_pref_behavior.js',
         ],
         'externs': [
           '../../../../../third_party/closure_compiler/externs/settings_private.js'
         ],
       },
       'includes': ['../../../../../third_party/closure_compiler/compile_js.gypi'],
     },
   ],
 }