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

chrome/browser/resources/md_history/app.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/html/cr/ui.html">
 <link rel="import" href="chrome://resources/html/cr/ui/command.html">
-<link rel="import" href="chrome://resources/polymer/v1_0/app-layout/app-drawer/app-drawer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/app-route/app-location.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/app-route/app-route.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-media-query/iron-media-query.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-pages/iron-pages.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-scroll-target-behavior/iron-scroll-target-behavior.html">
 <link rel="import" href="chrome://history/history_toolbar.html">
 <link rel="import" href="chrome://history/list_container.html">
-<link rel="import" href="chrome://history/synced_device_manager.html">
 <link rel="import" href="chrome://history/side_bar.html">
 <link rel="import" href="chrome://history/shared_style.html">
 <link rel="stylesheet" href="chrome://resources/css/md_colors.css">
 
+<!-- Lazy loaded: history-synced-device-manager, app-drawer. -->
+
 <dom-module id="history-app">
   <template>
     <style no-process>
       history-toolbar {
         background: var(--md-toolbar-color);
       }
     </style>
     <style include="shared-style">
       :host {
         display: block;
@@ skipping 18 matching lines @@
 
       :host-context([dir='rtl']) #content-side-bar {
         float: right;
       }
 
       #content,
       #content > * {
         height: 100%;
       }
 
+      #drawer:unresolved {
+        display: none;
+      }
+
       #drawer-header {
         align-items: center;
         border-bottom: 1px solid rgba(0, 0, 0, 0.08);
         display: flex;
         height: var(--toolbar-height);
         margin-bottom: 5px;
       }
 
       h1 {
         -webkit-padding-start: 24px;
@@ skipping 70 matching lines @@
         </history-side-bar>
       </app-drawer>
     </template>
 
     <iron-media-query query="(max-width: 1023px)"
         query-matches="{{hasDrawer_}}">
     </iron-media-query>
   </template>
   <script src="chrome://history/app.js"></script>
 </dom-module>