[MD History] Use proper shadows for cards.

chrome/browser/resources/md_history/grouped_list.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-collapse/iron-collapse.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
 <link rel="import" href="chrome://history/constants.html">
 <link rel="import" href="chrome://history/history_item.html">
 <link rel="import" href="chrome://history/history_list_behavior.html">
 <link rel="import" href="chrome://history/shared_style.html">
 
 <dom-module id="history-grouped-list">
   <template>
@@ skipping 22 matching lines @@
       .domain-count {
         color: rgb(151, 156, 160);
         padding-left: 10px;
       }
 
       .domain-heading-text {
         display: flex;
       }
 
       .group-container {
+        @apply(--card-box-shadow);
         background: #fff;
-        border: 1px solid var(--card-border-color);
-        border-bottom-width: 2px;
         border-radius: 2px;
         margin-bottom: var(--card-padding-between);
         max-width: var(--card-max-width);
         min-width: var(--card-min-width);
         width: 100%;
       }
 
       .card-title {
         margin-bottom: var(--card-first-last-item-padding);
       }
@@ skipping 55 matching lines @@
                 </template>
               </iron-collapse>
             </div>
           </template>
         </div>
       </template>
     </div>
     </template>
   <script src="chrome://history/grouped_list.js"></script>
 </dom-module>