MD Settings: Use a browser proxy from the languages page. Re-enable test.

chrome/browser/resources/settings/languages_page/languages_browser_proxy.js

+// Copyright 2017 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.
+
+/**
+ * @fileoverview A helper object used from the languages section
+ * to interact with the browser.
+ */
+
+cr.define('settings', function() {
+  /** @interface */
+  function LanguagesBrowserProxy() {}
+
+  LanguagesBrowserProxy.prototype = {
+// <if expr="chromeos or is_win">
+    /**
+     * Sets the prospective UI language to the chosen language. This won't
+     * affect the actual UI language until a restart.
+     * @param {string} languageCode
+     */
+    setProspectiveUILanguage: function(languageCode) {},
+
+    /** @return {!Promise<string>} */
+    getProspectiveUILanguage: function() {},
+// </if>
+
+    /** @return {!LanguageSettingsPrivate} */
+    getLanguageSettingsPrivate: function() {},
+
+// <if expr="chromeos">
+    /** @return {!InputMethodPrivate} */
+    getInputMethodPrivate: function() {},
+// </if>
+  };
+
+  /**
+   * @constructor
+   * @implements {settings.LanguagesBrowserProxy}
+   */
+  function LanguagesBrowserProxyImpl() {}
+  // The singleton instance_ is replaced with a test version of this wrapper
+  // during testing.
+  cr.addSingletonGetter(LanguagesBrowserProxyImpl);
+
+  LanguagesBrowserProxyImpl.prototype = {
+// <if expr="chromeos or is_win">
+    /** @override */
+    setProspectiveUILanguage: function(languageCode) {
+      chrome.send('setProspectiveUILanguage', [languageCode]);
+    },
+
+    /** @override */
+    getProspectiveUILanguage: function() {
+      return cr.sendWithPromise('getProspectiveUILanguage');
+    },
+// </if>
+
+    /** @override */
+    getLanguageSettingsPrivate: function() {
+      return /** @type {!LanguageSettingsPrivate} */ (
+          chrome.languageSettingsPrivate);
+    },
+
+// <if expr="chromeos">
+    /** @override */
+    getInputMethodPrivate: function() {
+      return /** @type {!InputMethodPrivate} */ (chrome.inputMethodPrivate);
+    },
+// </if>
+  };
+
+  return {
+    LanguagesBrowserProxy: LanguagesBrowserProxy,
+    LanguagesBrowserProxyImpl: LanguagesBrowserProxyImpl,
+  };
+});