Add an option in language settings for activating the IME menu.

chrome/browser/resources/options/language_options.js

Index: chrome/browser/resources/options/language_options.js
diff --git a/chrome/browser/resources/options/language_options.js b/chrome/browser/resources/options/language_options.js
index 0975c939746c1cd47a6d5cbc69047764030aa967..427700a91b8a7c5b302ef690ee2438b798020ab3 100644
--- a/chrome/browser/resources/options/language_options.js
+++ b/chrome/browser/resources/options/language_options.js
@@ -66,6 +66,14 @@ cr.define('options', function() {
    */
   var ENABLE_TRANSLATE = 'translate.enabled';
 
+  /**
+   * The preference is a boolean that activates/deactivates IME menu on the
+   * system shelf.
+   * @type {string}
+   * @const
+   */
+  var ACTIVATE_IME_MENU_PREF = 'settings.language.activate_ime_menu';
+
   /////////////////////////////////////////////////////////////////////////////
   // LanguageOptions class:
 
@@ -270,6 +278,11 @@ cr.define('options', function() {
       // Public session users cannot change the locale.
       if (cr.isChromeOS && UIAccountTweaks.loggedInAsPublicAccount())
         $('language-options-ui-language-section').hidden = true;
+
+      // Listen to check on 'activate-system-ime-menu' checkbox
+      var checkboxImeMenu = $('activate-system-ime-menu');

[Shu Chen, 2015/12/28 16:41:47]

pls put this behind a flag.

[Azure Wei, 2016/01/04 06:30:38]

Done.

+      checkboxImeMenu.addEventListener('click',
+          this.handleActivateSystemImeMenuCheckboxClick_.bind(this));
     },
 
     /**
@@ -1416,6 +1429,17 @@ cr.define('options', function() {
 
       return main;
     },
+
+    /**
+     * Handles activate-system-ime-menu checkbox's click event.
+     * @param {Event} e Click event.
+     * @private
+     */
+    handleActivateSystemImeMenuCheckboxClick_: function(e) {
+      var checkbox = e.target;
+      Preferences.setBooleanPref(ACTIVATE_IME_MENU_PREF,
+                                checkbox.checked, true);
+    },
   };
 
   /**