Extract language settings methods into a LanguageHelper interface

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

 // Copyright 2015 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 'settings-languages-page' is the settings page
  * for language and input method settings.
  *
  * @group Chrome Settings Elements
  * @element settings-languages-page
@@ skipping 25 matching lines @@
      * Read-only reference to the languages model provided by the
      * 'settings-languages' instance.
      * @type {LanguagesModel|undefined}
      */
     languages: {
       type: Object,
       notify: true,
     },
   },
 
+  /** @private {!LanguageHelper} */
+  languageHelper_: LanguageHelperImpl.getInstance(),
+
   /**
    * Handler for clicking a language on the main page, which selects the
    * language as the prospective UI language on Chrome OS and Windows.
    * @param {!{model: !{item: !LanguageInfo}}} e
    */
   onLanguageTap_: function(e) {
+    // Only change the UI language on platforms that allow it.
+    if (!cr.isChromeOS && !cr.isWindows)

[Dan Beam, 2015/12/01 04:17:44]

is there a rhyme or reason as to when we use cr.isThing vs. <if
expr="is_thing">?  i don't really see one...

[michaelpg, 2015/12/02 21:06:06]

yeah, i use <if> to exclude whole functions that don't make sense on other
platforms, and if() within functions.

<if> around functions makes them illegal to call on other platforms. <if> within
functions makes them weirder to reason about.

[Dan Beam, 2015/12/02 22:21:15]

fwiw:

  void DoThing() {
#if defined(OS_CHROME)
    ...
#endif
  }

is not uncommon in C++

+      return;
+
     // Taps on the paper-icon-button are handled in onShowLanguageDetailTap_.
     if (e.target.tagName == 'PAPER-ICON-BUTTON')
       return;
 
     // Set the prospective UI language. This won't take effect until a restart.
     if (e.model.item.language.supportsUI)
-      this.$.languages.setUILanguage(e.model.item.language.code);
+      this.languageHelper_.setUILanguage(e.model.item.language.code);
   },
 
   /**
    * Handler for enabling or disabling spell check.
    * @param {!{target: Element, model: !{item: !LanguageInfo}}} e
    */
   onSpellCheckChange_: function(e) {
-    this.$.languages.toggleSpellCheck(e.model.item.language.code,
-                                      e.target.checked);
+    this.languageHelper_.toggleSpellCheck(e.model.item.language.code,
+                                          e.target.checked);
   },
 
   /** @private */
   onBackTap_: function() {
     this.$.pages.back();
   },
 
   /**
    * Opens the Manage Languages page.
    * @private
@@ skipping 17 matching lines @@
   /**
    * Opens the Custom Dictionary page.
    * @private
    */
   onEditDictionaryTap_: function() {
     this.$.pages.setSubpageChain(['edit-dictionary']);
     this.forceRenderList_('settings-edit-dictionary-page');
   },
 </if>
 
+<if expr="chromeos or is_win">
   /**
+   * Checks whether the prospective UI language (the pref that indicates what
+   * language to use in Chrome) matches the current language. This pref is only
+   * on Chrome OS and Windows; we don't control the UI language elsewhere.
    * @param {string} languageCode The language code identifying a language.
    * @param {string} prospectiveUILanguage The prospective UI language.
    * @return {boolean} True if the given language matches the prospective UI
    *     pref (which may be different from the actual UI language).
    * @private
    */
-  isUILanguage_: function(languageCode, prospectiveUILanguage) {
-    return languageCode == this.$.languages.getProspectiveUILanguage();
+  isProspectiveUILanguage_: function(languageCode, prospectiveUILanguage) {
+    return languageCode == this.languageHelper_.getProspectiveUILanguage();
   },
+</if>
 
   /**
    * @param {string} id The input method ID.
    * @param {string} currentId The ID of the currently enabled input method.
    * @return {boolean} True if the IDs match.
    * @private
    */
   isCurrentInputMethod_: function(id, currentId) {
     assert(cr.isChromeOS);
     return id == currentId;
   },
 
   /**
    * HACK(michaelpg): This is necessary to show the list when navigating to
    * the sub-page. Remove this function when PolymerElements/neon-animation#60
    * is fixed.
    * @param {string} tagName Name of the element containing the <iron-list>.
    */
   forceRenderList_: function(tagName) {
     this.$$(tagName).$$('iron-list').fire('iron-resize');
   },
 });
 })();