Replace deprecated iron-flex-layout/classes with iron-flex-layout-class in MD Settings

chrome/browser/resources/settings/appearance_page/appearance_page.html

 <link rel="import" href="chrome://resources/html/i18n_behavior.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
-<link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/classes/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.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="/appearance_page/appearance_browser_proxy.html">
 <link rel="import" href="/controls/controlled_radio_button.html">
 <link rel="import" href="/controls/settings_dropdown_menu.html">
 <link rel="import" href="/controls/settings_input.html">
 <link rel="import" href="/controls/settings_radio_group.html">
 <link rel="import" href="/icons.html">
 <link rel="import" href="/route.html">
@@ skipping 22 matching lines @@
             <div class="secondary">$i18n{openWallpaperApp}</div>
           </div>
         </div>
         <div class="settings-box two-line"
             hidden="[[!pageVisibility.setTheme]]">
 </if>
 <if expr="not chromeos">
         <div class="settings-box two-line first"
             hidden="[[!pageVisibility.setTheme]]">
 </if>
-          <div class="layout horizontal center flex"
-              on-tap="openThemesGallery_" actionable>
-            <iron-icon icon="settings:palette"></iron-icon>
-            <div>
-              <div>$i18n{getThemes}</div>
-              <div class="secondary">[[themeSublabel_]]</div>
-            </div>
+          <iron-icon icon="settings:palette"></iron-icon>
+          <div class="start" on-tap="openThemesGallery_" actionable>
+            <div>$i18n{getThemes}</div>
+            <div class="secondary">[[themeSublabel_]]</div>
           </div>
           <template is="dom-if" if="[[allowResetTheme_]]">
             <div class="secondary-action">
               <paper-button id="resetTheme" on-tap="resetTheme_"
                   class="secondary-button">
                 $i18n{resetToDefaultTheme}
               </paper-button>
             </div>
           </template>
         </div>
@@ skipping 66 matching lines @@
             associated-control="[[$$('#customize-fonts-subpage-trigger')]]"
             page-title="$i18n{customizeFonts}">
           <settings-appearance-fonts-page prefs="{{prefs}}">
           </settings-appearance-fonts-page>
         </settings-subpage>
       </template>
     </settings-animated-pages>
   </template>
   <script src="appearance_page.js"></script>
 </dom-module>