[MD History] Small accessibility fixes.

chrome/browser/resources/md_history/history_toolbar.html

 <link rel="import" href="chrome://resources/html/polymer.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-icon-button/paper-icon-button.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-tabs/paper-tab.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-tabs/paper-tabs.html">
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_toolbar/cr_toolbar.html">
 <link rel="import" href="chrome://history/icons.html">
 <link rel="import" href="chrome://history/shared_style.html">
 
@@ skipping 117 matching lines @@
       <cr-toolbar id="main-toolbar" page-name="$i18n{title}"
           clear-label="$i18n{clearSearch}" search-prompt="$i18n{searchPrompt}"
           hidden$="[[itemsSelected_]]" spinner-active="[[spinnerActive]]"
           show-menu="[[hasDrawer]]" menu-label="$i18n{historyMenuButton}"
           on-search-changed="onSearchChanged_">
       </cr-toolbar>
       <template is="dom-if" if="[[itemsSelected_]]">
         <div id="overlay-wrapper" hidden$="[[!itemsSelected_]]">
           <div id="overlay-buttons">
             <paper-icon-button icon="cr:clear" id="cancel-icon-button"
-                on-tap="onClearSelectionTap_"></paper-icon-button>
+                on-tap="onClearSelectionTap_" title="$i18n{cancel}">
+            </paper-icon-button>
             <div id="number-selected">[[numberOfItemsSelected_(count)]]</div>
             <paper-button id="cancel-button" on-tap="onClearSelectionTap_">
               $i18n{cancel}
             </paper-button>
             <paper-button id="delete-button" on-tap="onDeleteTap_">
               $i18n{delete}
             </paper-button>
           </div>
         </div>
       </template>
@@ skipping 17 matching lines @@
               class="rtl-reversible"></paper-icon-button>
           <paper-icon-button icon="cr:chevron-right"
               alt="$i18n{rangeNext}" title="$i18n{rangeNext}"
               class="rtl-reversible"></paper-icon-button>
         </div>
       </div>
     </template>
   </template>
   <script src="chrome://history/history_toolbar.js"></script>
 </dom-module>