Added background page loader component extension.

chrome/browser/resources/chromeos/backloader/scripts/background.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.
+
+function Loader(pages) {
+  this.pages_ = pages;
+  this.pages_loaded_ = false;
+  this.loaded_count_ = false;
+}
+
+// Global instance.
+Loader.instance_ = null;
+
+// static.
+Loader.getInstance = function() {
+  if (!Loader.instance_)
+    Loader.instance_ = new Loader(g_pages);

[xiyuan, 2012/08/16 16:55:38]

Could you add a warning check to ensure g_pages is defined when running here?
e.g.

  if (!Loader.instance_) {
    if (!g_pages)
      console.log('Warning: Bad g_pages.');
    Loader.instance_ = new Loader(g_pages);
  }

[zel, 2012/08/16 17:17:22]

Done.

+
+  return Loader.instance_;
+};
+
+Loader.prototype = {
+  // Alarm name.
+  ALARM_NAME: 'CrOSBkgLoaderAlarm',
+  // Initial delay.
+  DELAY_IN_MINUTES: 1,
+  // Periodic wakeup delay.
+  PERIOD_IN_MINUTES: 60,
+  // Delayed closing of the background page once when all iframes are loaded.
+  UNLOAD_DELAY_IN_MS: 10000,
+
+  // Loader start up. Kicks off alarm initialization if needed.
+  initialize: function() {
+    chrome.alarms.onAlarm.addListener(this.onAlarm_.bind(this));
+    // Check if this alarm already exists, if not then create it.
+    chrome.alarms.get(this.ALARM_NAME, function(alarm) {
+      if (!alarm) {
+        chrome.alarms.create(this.ALARM_NAME,
+                             {delayInMinutes: this.DELAY_IN_MINUTES,
+                              periodInMinutes: this.PERIOD_IN_MINUTES});
+        window.close();
+        return;
+      }
+    }.bind(this));
+  },
+
+  onAlarm_: function(alarm) {
+    this.loadSubPages_();
+  },
+
+  onMessage_: function(event) {
+    var msg = event.data;
+    if (msg.method == 'validate') {
+      var msg = {

[xiyuan, 2012/08/16 16:55:38]

nit: could you use a different var name here, e.g. reply?

[zel, 2012/08/16 17:17:22]

Done.

+          method: 'validationResults',
+          os: 'ChromeOS'
+      };
+      event.source.postMessage(msg, event.origin);
+    } else {
+      console.log('#### Loader.onMessage_: unknown message');
+    }
+  },
+
+  loadSubPages_: function() {
+    if (this.pages_loaded_)
+      return;
+
+    window.addEventListener('message', this.onMessage_.bind(this), false);
+    for (i = 0; i < this.pages_.length; i++) {
+      this.loadPage_(i, this.pages_[i]);
+    }
+    this.pages_loaded_ = true;
+  },
+
+  loadPage_: function(index, pageUrl) {
+    var iframe = document.createElement('iframe');
+    iframe.onload = function() {
+      this.loaded_count_++;
+      if (this.loaded_count_ < this.pages_.length)
+        return;
+
+      // Delay closing.
+      setInterval(function() {
+        window.close();
+      }.bind(this), this.UNLOAD_DELAY_IN_MS);
+    }.bind(this);
+    iframe.src = pageUrl;
+    iframe.name = 'frame_' + index;
+    document.body.appendChild(iframe);
+  }
+};
+
+Loader.getInstance().initialize();

[xiyuan, 2012/08/16 16:55:38]

Could you wrap this into 

document.addEventListener('DOMContentLoaded', function(){
  Loader.getInstance().initialize();
});

so that we don't have a load dependency on page.js.