Implement the 'document.origin' accessor.

Source/core/dom/Document.idl

 /*
  * Copyright (C) 2006, 2007, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006, 2007 Samuel Weinig <sam@webkit.org>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 39 matching lines @@
 
     [MeasureAs=DocumentInputEncoding] readonly attribute DOMString? inputEncoding; // Removed from DOM4.
 
     [MeasureAs=DocumentXMLEncoding] readonly attribute DOMString? xmlEncoding; // Removed from DOM4.
     [RaisesException=Setter, MeasureAs=DocumentXMLVersion] attribute DOMString? xmlVersion; // Removed from DOM4.
     [RaisesException=Setter, MeasureAs=DocumentXMLStandalone] attribute boolean xmlStandalone; // Removed from DOM4.
 
     [RaisesException, CustomElementCallbacks, TypeChecking=Interface] Node adoptNode(Node node);
 
     [ImplementedAs=url] readonly attribute DOMString? documentURI;
+    readonly attribute DOMString origin;
 
     // DOM Level 2 Events (DocumentEvents interface)
 
     [RaisesException] Event createEvent(DOMString eventType);
 
     // DOM Level 2 Traversal and Range (DocumentRange interface)
 
     Range createRange();
 
     // DOM Level 2 Traversal and Range (DocumentTraversal interface)
@@ skipping 136 matching lines @@
     // TODO(davidben): This is a property so attaching a deprecation warning results in false positives when outputting
     // document in the console. It's possible http://crbug.com/43394 will resolve this.
     [MeasureAs=PrefixedPageVisibility, ImplementedAs=visibilityState] readonly attribute DOMString webkitVisibilityState;
     [MeasureAs=PrefixedPageVisibility, ImplementedAs=hidden] readonly attribute boolean webkitHidden;
 
     readonly attribute HTMLScriptElement currentScript;
 };
 
 Document implements GlobalEventHandlers;
 Document implements ParentNode;