MD Settings: Remove usage of deprecated iron-flex-layout.html.

chrome/browser/resources/settings/basic_page/basic_page.html

 <link rel="import" href="chrome://resources/html/polymer.html">
+<link rel="import" href="chrome://resources/cr_elements/hidden_style_css.html">
 <link rel="import" href="../appearance_page/appearance_page.html">
 <link rel="import" href="../controls/settings_idle_load.html">
 <link rel="import" href="../on_startup_page/on_startup_page.html">
 <link rel="import" href="../people_page/people_page.html">
 <link rel="import" href="../reset_page/reset_profile_banner.html">
 <link rel="import" href="../search_page/search_page.html">
 <link rel="import" href="../settings_page/main_page_behavior.html">
 <link rel="import" href="../settings_page/settings_page_visibility.html">
 <link rel="import" href="../settings_page/settings_section.html">
 <link rel="import" href="../settings_page_css.html">
 <link rel="import" href="../settings_vars_css.html">
 
 <if expr="chromeos">
 <link rel="import" href="../android_apps_page/android_apps_page.html">
 <link rel="import" href="../bluetooth_page/bluetooth_page.html">
 <link rel="import" href="../device_page/device_page.html">
 <link rel="import" href="../internet_page/internet_page.html">
 </if>
 
 <if expr="not chromeos">
 <link rel="import" href="../default_browser_page/default_browser_page.html">
 </if>
 
 <!-- TODO(michaelpg): Rename to something better than "basic" now that this page
      includes both the basic and advanced settings. -->
 <dom-module id="settings-basic-page">
   <template>
-    <style include="settings-page-styles">
+    <style include="settings-page-styles cr-hidden-style">
       :host([is-subpage-animating]) {
         /* Prevent an unwanted horizontal scrollbar when transitioning back from
          * a sub-page. */
         overflow: hidden;
       }
 
       #advancedToggle {
         --paper-button: {
           text-transform: none;
         }
@@ skipping 226 matching lines @@
                 section="reset">
               <settings-reset-page></settings-reset-page>
             </settings-section>
           </template>
         </div>
       </template>
     </template>
   </template>
   <script src="basic_page.js"></script>
 </dom-module>