MD History: Lazily load element files which are not needed for first paint

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-dropdown/iron-dropdown.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-icon-button/paper-icon-button-light.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_lazy_render/cr_lazy_render.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">
 
+<!-- Lazy loaded: iron-dropdown, paper-button, paper-icon-button-light,
+  paper-tab, paper-tabs. -->
+
 <dom-module id="history-toolbar">
   <template>
     <style include="shared-style">
       :host {
         color: #fff;
         display: block;
         transition: background-color 150ms;
         width: 100%;
       }
 
@@ skipping 32 matching lines @@
 
       :host([has-drawer]) cr-toolbar {
         --cr-toolbar-field-margin: 0;
       }
 
       cr-toolbar .more-actions {
         -webkit-margin-end: 12px;
       }
 
       #info-button {
+        /* Additional styles for unresolved <button>. */
+        background: none;
+        border: none;
+        color: inherit;
         height: 32px;
         margin: 6px;
+        outline: none;
+        padding: 0;
         width: 32px;
       }
 
       #info-button-icon {
         height: 20px;
         width: 20px;
       }
 
       iron-dropdown {
         margin-top: 28px;  /** Height of icon + 8px spacing. */
@@ skipping 150 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>