MD Settings: allow changing to GTK+ theme on Linux

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 cr.define('settings', function() {
   /** @interface */
   function AppearanceBrowserProxy() {}
 
   AppearanceBrowserProxy.prototype = {
     /**
-     * @return {!Promise<boolean>} Whether the theme may be reset.
+     * @param {string} themeId
+     * @return {!Promise<!chrome.management.ExtensionInfo>} Theme info.
      */
-    getResetThemeEnabled: assertNotReached,
+    getThemeInfo: assertNotReached,
 
 <if expr="chromeos">
     openWallpaperManager: assertNotReached,
 </if>
 
-    resetTheme: assertNotReached,
+    useDefaultTheme: assertNotReached,
+
+<if expr="is_linux and not chromeos">
+    useSystemTheme: assertNotReached,
+</if>
   };
 
   /**
    * @implements {settings.AppearanceBrowserProxy}
    * @constructor
    */
   function AppearanceBrowserProxyImpl() {}
 
   cr.addSingletonGetter(AppearanceBrowserProxyImpl);
 
   AppearanceBrowserProxyImpl.prototype = {
     /** @override */
-    getResetThemeEnabled: function() {
-      return cr.sendWithPromise('getResetThemeEnabled');
+    getThemeInfo: function(themeId) {
+      return new Promise(function(resolve) {
+        chrome.management.get(themeId, resolve);
+      });
     },
 
 <if expr="chromeos">
     /** @override */
     openWallpaperManager: function() {
       chrome.send('openWallpaperManager');
     },
 </if>
 
     /** @override */
-    resetTheme: function() {
-      chrome.send('resetTheme');
+    useDefaultTheme: function() {
+      chrome.send('useDefaultTheme');
     },
+
+<if expr="is_linux and not chromeos">
+    /** @override */
+    useSystemTheme: function() {
+      chrome.send('useSystemTheme');
+    },
+</if>
   };
 
   return {
     AppearanceBrowserProxy: AppearanceBrowserProxy,
     AppearanceBrowserProxyImpl: AppearanceBrowserProxyImpl,
   };
 });