MD Settings: don't allow supervised users to switch to GTK+ theme

chrome/browser/resources/settings/appearance_page/appearance_browser_proxy.js

Index: chrome/browser/resources/settings/appearance_page/appearance_browser_proxy.js
diff --git a/chrome/browser/resources/settings/appearance_page/appearance_browser_proxy.js b/chrome/browser/resources/settings/appearance_page/appearance_browser_proxy.js
index d5df59989eb0b908663ce655a966f38ccfdd6c32..e9cd6ec161be1bdf18aaf8a5e3c7591b72d16779 100644
--- a/chrome/browser/resources/settings/appearance_page/appearance_browser_proxy.js
+++ b/chrome/browser/resources/settings/appearance_page/appearance_browser_proxy.js
@@ -13,6 +13,9 @@ cr.define('settings', function() {
      */
     getThemeInfo: assertNotReached,
 
+    /** @return {boolean} Whether the current profile is supervised. */
+    isSupervised: assertNotReached,
+
 <if expr="chromeos">
     openWallpaperManager: assertNotReached,
 </if>
@@ -40,6 +43,11 @@ cr.define('settings', function() {
       });
     },
 
+    /** @override */
+    isSupervised: function() {
+      return loadTimeData.getBoolean('isSupervised');
+    },
+
 <if expr="chromeos">
     /** @override */
     openWallpaperManager: function() {