Build the language list just like we do in the C++ version.

chrome/browser/chromeos/dom_ui/language_options_handler.h

Index: chrome/browser/chromeos/dom_ui/language_options_handler.h
diff --git a/chrome/browser/chromeos/dom_ui/language_options_handler.h b/chrome/browser/chromeos/dom_ui/language_options_handler.h
index d8a957a57c5d5bac08bfcc043633c9e9e526d121..a5d04d4552a2780adcee11d245aaeb9816ed4b56 100644
--- a/chrome/browser/chromeos/dom_ui/language_options_handler.h
+++ b/chrome/browser/chromeos/dom_ui/language_options_handler.h
@@ -6,6 +6,7 @@
 #define CHROME_BROWSER_CHROMEOS_DOM_UI_LANGUAGE_OPTIONS_HANDLER_H_
 #pragma once
 
+#include "chrome/browser/chromeos/input_method/input_method_util.h"
 #include "chrome/browser/dom_ui/options_ui.h"
 
 class DictionaryValue;
@@ -26,14 +27,16 @@ class LanguageOptionsHandler : public OptionsPageUIHandler {
   virtual void RegisterMessages();
 
  private:
-  // Gets the list of input methods. The return value will look like:
+  // Gets the list of input methods from the given input descriptors.
+  // The return value will look like:
   // [{'id': 'pinyin', 'displayName': 'Pinyin', 'languageCode': 'zh-CW'}, ...]
-  ListValue* GetInputMethodList();
+  ListValue* GetInputMethodList(const InputMethodDescriptors& descriptors);
 
-  // Gets the list of languages. The return value will look like:
+  // Gets the list of languages from the given input descriptors.
+  // The return value will look like:
   // [{'code': 'fi', 'displayName': 'Finnish', 'nativeDisplayName': 'suomi'},
   //  ...]
-  ListValue* GetLanguageList();
+  ListValue* GetLanguageList(const InputMethodDescriptors& descriptors);
 
   // Called when the UI language is changed.
   // |value| will be the language code as string (ex. "fr").