Send an ack msg to a parent iframe when setting iframe ids for ChromeVox.

chrome/browser/resources/chromeos/chromevox/common/interframe.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.
 
 /**
  * @fileoverview Tools for interframe communication. To use this class, every
  * window that wants to communicate with its child iframes should enumerate
  * them using document.getElementsByTagName('iframe'), create an ID to
  * associate with that iframe, then call cvox.Interframe.sendIdToIFrame
  * on each of them. Then use cvox.Interframe.sendMessageToIFrame to send
@@ skipping 23 matching lines @@
 
 /**
  * The message used to set the ID of a child frame so that it can send replies
  * to its parent frame.
  * @type {string}
  * @const
  */
 cvox.Interframe.SET_ID = 'cvox.INTERFRAME_SET_ID';
 
 /**
+ * The message used by a child frame to acknowledge an id was set (sent to its
+ * parent frame.
+ * @type {string}
+ * @const
+ */
+cvox.Interframe.ACK_SET_ID = 'cvox.INTERFRAME_ACK_SET_ID';
+
+/**
  * The ID of this window (relative to its parent farme).
  * @type {number|string|undefined}
  */
 cvox.Interframe.id;
 
 /**
  * Array of functions that have been registered as listeners to interframe
  * messages send to this window.
  * @type {Array.<function(Object)>}
  */
 cvox.Interframe.listeners = [];
 
 /**
+ * Maps an id to a function which gets called when a frame first sends an ack
+ * for a set id msg.
+ @dict {!Object.<number|string, function()>}
+ * @private
+ */
+cvox.Interframe.idToCallback_ = {};
+
+/**
  * Flag for unit testing. When false, skips over iframe.contentWindow check
  * in sendMessageToIframe. This is needed because in the wild, ChromeVox may
  * not have access to iframe.contentWindow due to the same-origin security
  * policy. There is no reason to set this outside of a test.
  * @type {boolean}
  */
 cvox.Interframe.allowAccessToIframeContentWindow = true;
 
 /**
  * Initializes the cvox.Interframe module. (This is called automatically.)
  */
 cvox.Interframe.init = function() {
   cvox.Interframe.messageListener = function(event) {
     if (typeof event.data === 'string' &&
         event.data.indexOf(cvox.Interframe.IF_MSG_PREFIX) == 0) {
       var suffix = event.data.substr(cvox.Interframe.IF_MSG_PREFIX.length);
       var message = /** @type {Object} */ (
           cvox.ChromeVoxJSON.parse(suffix));
       if (message['command'] == cvox.Interframe.SET_ID) {
         cvox.Interframe.id = message['id'];
+        message['command'] = cvox.Interframe.ACK_SET_ID;
+        cvox.Interframe.sendMessageToParentWindow(message);
+      } else if (message['command'] == cvox.Interframe.ACK_SET_ID) {
+        cvox.Interframe.id = message['id'];
+        var callback = cvox.Interframe.idToCallback_[cvox.Interframe.id];
+        callback();
       }
       for (var i = 0, listener; listener = cvox.Interframe.listeners[i]; i++) {
         listener(message);
       }
     }
     return false;
   };
   window.addEventListener('message', cvox.Interframe.messageListener, true);
 };
 
@@ skipping 102 matching lines @@
   window.location.href =
       'javascript:window.parent.postMessage(\'' +
       encodeURI(encodedMessage) + '\', \'*\');';
 };
 
 /**
  * Send the given ID to a child iframe.
  * @param {number|string} id The ID you want to receive in replies from
  *     this iframe.
  * @param {HTMLIFrameElement} iframe The iframe to assign.
+ * @param {function()=} opt_callback Called when a ack msg arrives from the
+ *frame.
  */
-cvox.Interframe.sendIdToIFrame = function(id, iframe) {
+cvox.Interframe.sendIdToIFrame = function(id, iframe, opt_callback) {
+  if (opt_callback) {
+    cvox.Interframe.idToCallback_[id] = opt_callback;
+  }
   var message = {'command': cvox.Interframe.SET_ID, 'id': id};
   cvox.Interframe.sendMessageToIFrame(message, iframe);
 };
 
 /**
  * Returns true if inside iframe
  * @return {boolean} true if inside iframe.
  */
 cvox.Interframe.isIframe = function() {
   return (window != window.parent);
 };
 
 cvox.Interframe.init();