[MD History] Small accessibility fixes.

chrome/browser/resources/md_history/history_item.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/iron-icon/iron-icon.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-button/paper-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-checkbox/paper-checkbox.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button-light.html">
 <link rel="import" href="chrome://resources/html/icon.html">
 <link rel="import" href="chrome://resources/html/util.html">
 <link rel="import" href="chrome://history/browser_service.html">
 <link rel="import" href="chrome://history/constants.html">
@@ skipping 131 matching lines @@
 
     <div id="sizing-container">
       <div id="main-container">
         <div id="background"></div>
         <div id="date-accessed" class="card-title">
           [[cardTitle_(numberOfItems, item.dateRelativeDay, searchTerm)]]
         </div>
         <div id="item-container">
           <paper-checkbox id="checkbox" on-mousedown="onCheckboxMousedown_"
               on-click="onCheckboxSelected_" checked="{{selected}}"
-              disabled="[[selectionNotAllowed_()]]">
+              disabled="[[selectionNotAllowed_()]]"
+              aria-label$="[[getEntrySummary_(item)]]">
           </paper-checkbox>
           <span id="time-accessed">[[item.readableTimestamp]]</span>
           <div class="website-icon" id="icon"></div>
           <div id="title-and-domain">
             <a href="[[item.url]]" id="title" class="website-title"
                 title="[[cropItemTitle_(item.title)]]"
                 on-click="onLinkClick_" on-contextmenu="onLinkRightClick_">
               <history-searched-label title="[[cropItemTitle_(item.title)]]"
                   search-term="[[searchTerm]]"></history-searched-label>
             </a>
@@ skipping 14 matching lines @@
             <div></div>
             <div></div>
           </button>
         </div>
         <div id="time-gap-separator" hidden="[[!hasTimeGap]]"></div>
       </div>
     </div>
   </template>
   <script src="chrome://history/history_item.js"></script>
 </dom-module>