[DevTools] Extract part of DevTools into inspector app.

Source/devtools/front_end/platform/DOMExtension.js

 /*
  * Copyright (C) 2007 Apple Inc.  All rights reserved.
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 759 matching lines @@
  */
 function isEnterKey(event) {
     // Check if in IME.
     return event.keyCode !== 229 && event.keyIdentifier === "Enter";
 }
 
 function consumeEvent(e)
 {
     e.consume();
 }
+
+/**
+ * @param {!function()} callback
+ * @suppressGlobalPropertiesCheck
+ */
+function runOnWindowLoad(callback)
+{
+    /**
+     * @suppressGlobalPropertiesCheck
+     */
+    function windowLoaded()
+    {
+        window.removeEventListener("DOMContentLoaded", windowLoaded, false);
+        callback();
+    }
+
+    if (document.readyState === "complete")
+        callback();
+    else
+        window.addEventListener("DOMContentLoaded", windowLoaded, false);
+}