Implement chrome.languageSettingsPrivate custom spell check functions

chrome/common/extensions/api/language_settings_private.idl

Index: chrome/common/extensions/api/language_settings_private.idl
diff --git a/chrome/common/extensions/api/language_settings_private.idl b/chrome/common/extensions/api/language_settings_private.idl
index 8b1a795a21a0c31f33064e1c450d651bd4ffe54e..30958c56db0f0f7795f71251f0992f62b9631f36 100644
--- a/chrome/common/extensions/api/language_settings_private.idl
+++ b/chrome/common/extensions/api/language_settings_private.idl
@@ -88,9 +88,15 @@ namespace languageSettingsPrivate {
     static void getSpellcheckDictionaryStatuses(
         GetSpellcheckDictionaryStatusesCallback callback);
 
-    // Gets the custom spell check words.
+    // Gets the custom spell check words, in sorted order.
     static void getSpellcheckWords(GetSpellcheckWordsCallback callback);
 
+    // Adds a word to the custom dictionary.
+    static void addSpellcheckWord(DOMString word);
+
+    // Removes a word from the custom dictionary.
+    static void removeSpellcheckWord(DOMString word);
+
     // Gets the translate target language (in most cases, the display locale).
     static void getTranslateTargetLanguage(
         GetTranslateTargetLanguageCallback callback);