Hotword Private API: Add function and event to query the existence of a speaker model

chrome/test/data/extensions/api_test/hotword_private/speakerModelExistsResultFalse/test.js

 // Copyright 2014 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.
 
 chrome.test.runTests([
-  function setEnabledFalse() {
-    chrome.hotwordPrivate.setEnabled(
+  function speakerModelExistsResultFalse() {
+    chrome.hotwordPrivate.speakerModelExistsResult(
         false, chrome.test.callbackPass(function() {
           chrome.test.sendMessage("ready");
         }));
   }
 ]);