Modify languageSettingsPrivate IDL and flesh out stub implementation

extensions/browser/extension_event_histogram_value.h

Index: extensions/browser/extension_event_histogram_value.h
diff --git a/extensions/browser/extension_event_histogram_value.h b/extensions/browser/extension_event_histogram_value.h
index 03bd28c0ab907ebd70024f74d00c5d12999cc745..ea9191bd4a98e876ad367f60924d27b2b854e826 100644
--- a/extensions/browser/extension_event_histogram_value.h
+++ b/extensions/browser/extension_event_histogram_value.h
@@ -394,7 +394,10 @@ enum HistogramValue {
   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