MD Settings: make custom UIs look "actionable"

chrome/browser/resources/settings/default_browser_page/default_browser_page.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="/icons.html">
 <link rel="import" href="/settings_shared_css.html">
 
 <dom-module id="settings-default-browser-page">
   <template>
     <style include="settings-shared">
       .error-icon {
         color: var(--settings-error-color);
       }
     </style>
     <div class="settings-box first two-line">
       <template is="dom-if" if="[[showButton_]]">
-        <div class="start" on-tap="onSetDefaultBrowserTap_">
+        <div class="start" on-tap="onSetDefaultBrowserTap_" actionable>
           <div>$i18n{defaultBrowser}</div>
           <div class="secondary">$i18n{defaultBrowserMakeDefault}</div>
         </div>
         <template is="dom-if" if="[[showError_]]">
           <iron-icon icon="settings:error" class="error-icon"
               title="$i18n{unableToSetDefaultBrowser}"></iron-icon>
         </template>
       </template>
       <template is="dom-if" if="[[!showButton_]]">
         <div class="secondary">[[message_]]</div>
       </template>
     </div>
   </template>
   <script src="default_browser_page.js"></script>
 </dom-module>