MD History: Simplify flex layout in <history-list>

chrome/browser/resources/md_history/app.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-pages/iron-pages.html">
 <link rel="import" href="chrome://history/grouped_list.html">
 <link rel="import" href="chrome://history/history_list.html">
 <link rel="import" href="chrome://history/history_toolbar.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">
 
 <dom-module id="history-app">
   <!-- TODO(calamity): work around this deprecated import style -->
   <template>
     <style no-process>
       history-toolbar {
         background: var(--md-toolbar-color);
       }
     </style>
     <style include="shared-style">
       :host {
-        display: flex;
-        flex-direction: column;
+        display: block;
+        height: 100%;
         min-width: 800px;
-      }
-
-      #main-container {
-        display: flex;
-        flex: 1 0 0;
         overflow: hidden;
       }
 
-      history-list,
-      history-synced-device-manager,
-      history-grouped-list {
-        flex: 1 0 0;
+      /* Sizing this with flex causes slow load performance, see
+         crbug.com/618153. */
+      #main-container {
+        height: calc(100% - var(--toolbar-height));
       }
 
-      #content {
-        display: flex;
-        flex: 1 0 0;
-        overflow: hidden;
+      :host([grouped_]) #main-container {
+        height: calc(100% - var(--toolbar-grouped-height));
+      }
+
+      #content,
+      #content > * {
+        height: 100%;
+      }
+
+      #history-side-bar {
+        float: left;
       }
     </style>
     <history-toolbar id="toolbar"
         spinner-active="[[shouldShowSpinner_(queryState_.querying,
                                              queryState_.incremental,
                                              queryState_.searchTerm)]]"
         is-grouped-mode="{{grouped_}}"
         grouped-range="{{queryState_.range}}"
         search-term="{{queryState_.searchTerm}}"
         query-start-time="[[queryState_.info.queryStartTime]]"
@@ skipping 19 matching lines @@
           <history-synced-device-manager id="history-synced-device-manager"
               session-list="[[queryState_.sessionList]]"
               searched-term=[[queryState_.info.term]]>
           </history-synced-device-manager>
         </template>
       </iron-pages>
     </div>
   </template>
   <script src="chrome://history/app.js"></script>
 </dom-module>