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

chrome/browser/resources/settings/people_page/people_page.html

 <link rel="import" href="chrome://resources/cr_elements/cr_dialog/cr_dialog.html">
 <link rel="import" href="chrome://resources/cr_elements/cr_expand_button/cr_expand_button.html">
 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/html/icon.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/html/util.html">
 <link rel="import" href="chrome://resources/html/web_ui_listener_behavior.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-collapse/iron-collapse.html">
+<link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/iron-flex-layout-classes.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/neon-animation/neon-animatable.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-checkbox/paper-checkbox.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-icon-button/paper-icon-button-light.html">
 <link rel="import" href="../controls/settings_toggle_button.html">
 <link rel="import" href="sync_page.html">
 <link rel="import" href="profile_info_browser_proxy.html">
 <link rel="import" href="sync_browser_proxy.html">
 <link rel="import" href="../route.html">
 <link rel="import" href="../settings_page/settings_animated_pages.html">
 <link rel="import" href="../settings_page/settings_subpage.html">
 <link rel="import" href="../settings_shared_css.html">
 
 <if expr="chromeos">
 <link rel="import" href="change_picture.html">
 <link rel="import" href="fingerprint_list.html">
 <link rel="import" href="lock_screen.html">
 <link rel="import" href="lock_state_behavior.html">
 <link rel="import" href="users_page.html">
 </if>
 <if expr="not chromeos">
 <link rel="import" href="import_data_dialog.html">
 <link rel="import" href="manage_profile.html">
 </if>
 
 <dom-module id="settings-people-page">
   <template>
-    <style include="settings-shared">
+    <style include="settings-shared iron-flex">
       setting-box.middle {
         /* Per spec, middle text is indented 20px in this section. */
         -webkit-margin-start: 20px;
       }
 
       #profile-icon {
         background-position: center;
         background-repeat: no-repeat;
         background-size: cover;
         border-radius: 20px;
@@ skipping 294 matching lines @@
 
     <template is="dom-if" if="[[showImportDataDialog_]]" restamp>
       <settings-import-data-dialog prefs="{{prefs}}"
           on-close="onImportDataDialogClosed_">
       </settings-import-data-dialog>
     </template>
 
   </template>
   <script src="people_page.js"></script>
 </dom-module>