[MD History] Color tweaks.

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://resources/polymer/v1_0/paper-styles/shadow.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">
@@ skipping 14 matching lines @@
       }
 
       .domain-heading {
         align-items: center;
         display: flex;
         height: var(--item-height);
         padding: 0 20px;
       }
 
       .domain-count {
-        color: rgb(151, 156, 160);
+        color: var(--secondary-text-color);
         padding-left: 10px;
       }
 
       .domain-heading-text {
         display: flex;
       }
 
       .group-container {
         @apply(--shadow-elevation-2dp);
         background: #fff;
@@ skipping 64 matching lines @@
                 </template>
               </iron-collapse>
             </div>
           </template>
         </div>
       </template>
     </div>
     </template>
   <script src="chrome://history/grouped_list.js"></script>
 </dom-module>