Modify languageSettingsPrivate IDL and flesh out stub implementation

extensions/browser/extension_event_histogram_value.h

 // 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.
 
 #ifndef EXTENSIONS_BROWSER_EXTENSION_EVENT_HISTOGRAM_VALUE_H_
 #define EXTENSIONS_BROWSER_EXTENSION_EVENT_HISTOGRAM_VALUE_H_
 
 namespace extensions {
 namespace events {
 
@@ skipping 376 matching lines @@
   WEB_VIEW_INTERNAL_ON_LOAD_START,
   WEB_VIEW_INTERNAL_ON_LOAD_STOP,
   WEB_VIEW_INTERNAL_ON_NEW_WINDOW,
   WEB_VIEW_INTERNAL_ON_PERMISSION_REQUEST,
   WEB_VIEW_INTERNAL_ON_RESPONSE_STARTED,
   WEB_VIEW_INTERNAL_ON_RESPONSIVE,
   WEB_VIEW_INTERNAL_ON_SIZE_CHANGED,
   WEB_VIEW_INTERNAL_ON_UNRESPONSIVE,
   WEB_VIEW_INTERNAL_ON_ZOOM_CHANGE,
   GUEST_VIEW_INTERNAL_ON_RESIZE,
-
+  LANGUAGE_SETTINGS_PRIVATE_ON_INPUT_METHOD_ADDED,
+  LANGUAGE_SETTINGS_PRIVATE_ON_INPUT_METHOD_REMOVED,
+  LANGUAGE_SETTINGS_PRIVATE_ON_SPELLCHECK_DICTIONARIES_CHANGED,
+  LANGUAGE_SETTINGS_PRIVATE_ON_CUSTOM_DICTIONARY_CHANGED,
   // Last entry: Add new entries above, then run:
   // python tools/metrics/histograms/update_extension_histograms.py
   ENUM_BOUNDARY
 };
 
 }  // namespace events
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_EXTENSION_EVENT_HISTOGRAM_VALUE_H_