MD Settings: Show "Set date and time" button when relevant

chrome/browser/resources/settings/settings_shared_css.html

 <link rel="import" href="chrome://resources/cr_elements/shared_style_css.html">
 <link rel="import" href="/settings_vars_css.html">
 
 <!-- Common styles for Material Design settings. -->
 <dom-module id="settings-shared">
   <template>
     <style include="cr-shared-style">
+      /* Included here so we don't have to include "iron-positioning" in every
+       * stylesheet. See crbug.com/498405. */
+      [hidden] {
+        display: none !important;
+      }
+
       button[is='paper-icon-button-light'] {
         -webkit-margin-end: -8px;  /* Allow ripple to overlap the end. */
         -webkit-margin-start: 16px;
         background-position: center;
         background-repeat: no-repeat;
         background-size: var(--settings-icon-size);
         flex-shrink: 0;
         height: var(--settings-icon-ripple-size);
         width: var(--settings-icon-ripple-size);
       }
@@ skipping 412 matching lines @@
       /* Turns the arrow direction downwards, when the bubble is placed above
        * the anchor element */
       .search-bubble-innards.above::after {
         -webkit-transform: rotate(-135deg);
         bottom: -5px;
         top: auto;
       }
     </style>
   </template>
 </dom-module>