Add chrome.inputMethodPrivate.onImeMenuActivationChanged API.

chrome/test/data/extensions/api_test/input_method/ime_menu/background.js

+// Copyright 2016 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.inputMethodPrivate.getInputMethodConfig(function(config) {
+  chrome.test.assertTrue(config["isImeMenuActivated"]);
+  chrome.test.sendMessage('config_ready');
+});
+
+// We just add the listener without receiving any event at first time. The test
+// continues in input_method_apitest_chromeos.cc to trigger the event, and
+// succeeds after getting the 'event_ready' message.
+chrome.inputMethodPrivate.onImeMenuActivationChanged.addListener(
+  function(isActive) {
+    chrome.test.assertFalse(isActive);
+    // Wait for the 'event_ready' message in
+    // ExtensionInputMethodApiTest.ImeMenuActivation.
+    chrome.test.sendMessage('event_ready');
+});