MD Settings: long dialog body should have overscroll line.

chrome/browser/resources/settings/languages_page/add_languages_dialog.html

+<link rel="import" href="chrome://resources/cr_elements/cr_scrollable_behavior.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_dialog/cr_dialog.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-list/iron-list.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-checkbox/paper-checkbox.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="languages.html">
 <link rel="import" href="../settings_page/settings_subpage_search.html">
 <link rel="import" href="../settings_shared_css.html">
 
 <dom-module id="settings-add-languages-dialog">
@@ skipping 15 matching lines @@
         flex: 1;
       }
 
       .ripple-padding {
         /* Create a little extra space for checkbox ink ripple to flow into. */
         -webkit-padding-start: 20px;
       }
     </style>
     <dialog is="cr-dialog" id="dialog" close-text="$i18n{close}">
       <div class="title">$i18n{addLanguagesDialogTitle}</div>
-      <div class="body">
+      <div class="body" scrollable>
         <settings-subpage-search label="[[searchLabel]]"
             on-search-changed="onSearchChanged_" autofocus>
         </settings-subpage-search>
         <iron-list class="ripple-padding" scroll-target="[[$$('.body')]]"
             items="[[getLanguages_(
                 languages.supported, languages.enabled.*, filterValue_)]]">
           <template>
             <paper-checkbox class="list-item" checked="[[willAdd_(item.code)]]"
                 title$="[[item.nativeDisplayName]]"
                 on-change="onLanguageCheckboxChange_"
@@ skipping 11 matching lines @@
           <paper-button class="action-button" on-tap="onActionButtonTap_"
               disabled="[[disableActionButton_]]">
             $i18n{add}
           </paper-button>
         </div>
       </div>
     </dialog>
   </template>
   <script src="add_languages_dialog.js"></script>
 </dom-module>