MD History: Add lazy-render element for simple lazy initialization.

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/iron-icons/hardware-icons.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">
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         transform: rotate(180deg);
       }
     </style>
     <div id="toolbar-container">
       <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]]"
           on-search-changed="onSearchChanged_">
       </cr-toolbar>
-      <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>
-          <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_">
-            $i18n{delete}
-          </paper-button>
+      <template is="dom-if" if="[[itemsSelected_]]">
+        <div id="overlay-wrapper" hidden$="[[!itemsSelected_]]">
+          <div id="overlay-buttons">
+            <paper-icon-button icon="cr:clear" id="cancel-icon-button"
+                on-tap="onClearSelectionTap_"></paper-icon-button>
+            <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_">
+              $i18n{delete}
+            </paper-button>
+          </div>
         </div>
-      </div>
+      </template>
     </div>
     <template is="dom-if" if="[[isGroupedMode]]">
       <div id="grouped-buttons-container">
         <paper-tabs attr-for-selected="value" selected="{{groupedRange}}"
             id="grouped-range-buttons">
           <paper-tab value="0">$i18n{rangeAllTime}</paper-tab>
           <paper-tab value="1">$i18n{rangeWeek}</paper-tab>
           <paper-tab value="2">$i18n{rangeMonth}</paper-tab>
         </paper-tabs>
         <div id="grouped-nav-container">
           <span id="grouped-date">
             {{getHistoryInterval_(queryStartTime, queryEndTime)}}
           </span>
           <paper-icon-button icon="history:today" alt="$i18n{rangeToday}"
               title="$i18n{rangeToday}"></paper-icon-button>
           <paper-icon-button icon="history:chevron-left"
               alt="$i18n{rangePrevious}" title="$i18n{rangePrevious}"
               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>