Add a parameter that specifies whether onKeyEvent is asynchronous

chrome/renderer/resources/extensions/input.ime_custom_bindings.js

 // Copyright (c) 2012 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.
 
 // Custom bindings for the input ime API. Only injected into the
 // v8 contexts for extensions which have permission for the API.
 
 var chromeHidden = requireNative('chrome_hidden').GetChromeHidden();
 
 chromeHidden.registerCustomHook('input.ime', function() {
   chrome.input.ime.onKeyEvent.dispatchToListener = function(callback, args) {
     var engineID = args[0];
     var keyData = args[1];
 
     var result = false;
     try {
       result = chrome.Event.prototype.dispatchToListener(callback, args);
     } catch (e) {
       console.error('Error in event handler for onKeyEvent: ' + e.stack);
     }
-    chrome.input.ime.eventHandled(keyData.requestId, result);
+    if (!chrome.input.ime.onKeyEvent.async)
+      chrome.input.ime.keyEventHandled(keyData.requestId, result);
+  };
+
+  chrome.input.ime.onKeyEvent.addListener = function(cb, opt_extraInfo) {
+    chrome.input.ime.onKeyEvent.async = false;
+    if (opt_extraInfo instanceof Array) {
+      for (var i = 0; i < opt_extraInfo.length; ++i) {
+        if (opt_extraInfo[i] == "async") {
+          chrome.input.ime.onKeyEvent.async = true;
+        }
+      }
+    }
+    chrome.Event.prototype.addListener.call(this, cb, null);
   };
 });