MD History: Add spinners when new data is loading or searching

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/iron-flex-layout/iron-flex-layout.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/cr_elements/cr_search_field/cr_search_field.html">
 <link rel="import" href="chrome://history/shared_style.html">
 
 <dom-module id="history-toolbar">
   <template>
     <style include="shared-style"></style>
@@ skipping 23 matching lines @@
         @apply(--layout-flex);
         font-size: 16px;
         font-weight: 400;
         padding-left: 24px;
       }
 
       #search-input {
         -webkit-padding-end: 20px;
       }
 
+      #searching-spinner {
+        top: 15px;

[tsergeant, 2016/04/15 05:14:50]

Is this necessary?

[lshang, 2016/04/18 00:29:00]

Done.

+      }
+
+      paper-spinner.search {
+        height: 20px;
+        width: 20px;
+      }
+
       #items {
         margin: 0 auto;
         max-width: var(--card-max-width);
       }
 
       #number-selected {
         @apply(--layout-flex);
       }
 
       paper-icon-button {
@@ skipping 24 matching lines @@
         min-width: 100px;
       }
 
       #back-padding {
         flex: 1 1 0;
       }
     </style>
     <div id="toolbar-container">
       <div id="main-content" hidden$="[[itemsSelected_]]">
         <h1 id="title">$i18n{title}</h1>
+        <div id="searching-spinner"  hidden$="[[!searching_]]">
+          <paper-spinner class="search" alt="searching in history" active>

[tsergeant, 2016/04/15 05:14:50]

Same comment here about localization.

However, since the alt-text is only used by screen readers, depending on how the
screen reader works, it might not be necessary to set the alt-text on both
spinners -- it might work fine if you leave one empty.

[lshang, 2016/04/18 00:29:00]

Done.

+          </paper-spinner>
+        </div>
         <cr-search-field id="search-input" label="$i18n{search}"
             clear-label="$i18n{clearSearch}">
         </cr-search-field>
       </div>
 
       <div id="items" hidden$="[[!itemsSelected_]]">
         <paper-icon-button icon="clear" id="cancel-icon-button"
             on-tap="onClearSelectionTap_"></paper-icon-button>
         <div id="number-selected">[[numberOfItemsSelected_(count)]]</div>
         <paper-button id="cancel-button" on-tap="onClearSelectionTap_">
@@ skipping 11 matching lines @@
         <paper-button on-tap="onClearBrowsingDataTap_"
             id="clear-browsing-data-button">
           $i18n{clearBrowsingData}
         </paper-button>
       </div>
       <div id="back-padding"></div>
     </div>
   </template>
   <script src="chrome://history/history_toolbar.js"></script>
 </dom-module>