[MD History] Implement grouped history UI.

chrome/browser/resources/md_history/synced_device_card.html

 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/shadow.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://resources/polymer/v1_0/iron-flex-layout/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/html/icon.html">
 <link rel="import" href="chrome://history/shared_style.html">
 
 <dom-module id="history-synced-device-card">
   <template>
     <style include="shared-style">
       :host {
         @apply(--layout-center);
         @apply(--layout-vertical);
-        padding: 0 var(--card-padding-side) 20px;
+        padding: 0 var(--card-padding-side) var(--card-padding-between);
       }
 
       #card-heading {
         @apply(--layout-justified);
         cursor: pointer;
       }
 
       #icon {
         -webkit-margin-start: 20px;
       }
@@ skipping 72 matching lines @@
           </template>
           <div class="item-container">
             <p on-tap="openAllTabs_" id="open-tabs">$i18n{openAll}</p>
           </div>
         </div>
       </iron-collapse>
     </div>
   </template>
   <script src="chrome://history/synced_device_card.js"></script>
 </dom-module>