Added top level definition to Window.

sdk/lib/html/dart2js/html_dart2js.dart

 library html;
 
 import 'dart:isolate';
 import 'dart:json';
 import 'dart:svg' as svg;
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // DO NOT EDIT
@@ skipping 21989 matching lines @@
 
 class _XSLTProcessorFactoryProvider {
   static XSLTProcessor createXSLTProcessor() =>
       JS('XSLTProcessor', 'new XSLTProcessor()' );
 }
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 
+/**
+ * An object representing the top-level context object for web scripting.
+ *
+ * In a web browser, a [Window] object represents the actual browser window.
+ * In a multi-tabbed browser, each tab has its own [Window] object. A [Window]
+ * is the container that displays a [Document]'s content. All web scripting
+ * happens within the context of a [Window] object.
+ *
+ * **Note:** This class represents any window, whereas [LocalWindow] is
+ * used to access the properties and content of the current window.
+ *
+ * See also:
+ *
+ * * [DOM Window](https://developer.mozilla.org/en-US/docs/DOM/window) from MDN.
+ * * [Window](http://www.w3.org/TR/Window/) from the W3C.
+ */
 abstract class Window {
   // Fields.
   Location get location;
   History get history;
 
   bool get closed;
   Window get opener;
   Window get parent;
   Window get top;
 
@@ skipping 2834 matching lines @@
     if (length < 0) throw new ArgumentError('length');
     if (start < 0) throw new RangeError.value(start);
     int end = start + length;
     if (end > a.length) throw new RangeError.value(end);
     for (int i = start; i < end; i++) {
       accumulator.add(a[i]);
     }
     return accumulator;
   }
 }