Allow component IME extension use app.window and add 'ime' window type for app window

extensions/renderer/resources/app_window_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 binding for the app_window API.
 
 var appWindowNatives = requireNative('app_window_natives');
 var runtimeNatives = requireNative('runtime');
 var Binding = require('binding').Binding;
 var Event = require('event_bindings').Event;
@@ skipping 384 matching lines @@
     if (value === null)
       constraints[key] = 0;
   });
 
   currentWindowInternal.setSizeConstraints(boundsType, constraints);
 }
 
 exports.binding = appWindow.generate();
 exports.onAppWindowClosed = onAppWindowClosed;
 exports.updateAppWindowProperties = updateAppWindowProperties;
-exports.appWindowShownForTests = onAppWindowShownForTests;
+exports.appWindowShownForTests = onAppWindowShownForTests;