Added some more documentation to top level Window.

tools/dom/templates/html/dartium/html_dartium.darttemplate

 // 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
 // Auto-generated dart:html library.
 
 /// The Dart HTML library.
 ///
 /// For examples, see
@@ skipping 41 matching lines @@
 part '$AUXILIARY_DIR/Isolates.dart';
 part '$AUXILIARY_DIR/Microtask.dart';
 part '$AUXILIARY_DIR/Serialization.dart';
 part '$AUXILIARY_DIR/_ListIterators.dart';
 
 part '$AUXILIARY_DIR/native_DOMPublic.dart';
 part '$AUXILIARY_DIR/native_DOMImplementation.dart';
 
 Window _window;
 
+/**
+ * Top-level container for a web page, which is usually a browser tab or window.
+ *
+ * Each web page loaded in the browser has its own [Window], which is a
+ * container for the web page.
+ *
+ * If the web page has any `<iframe>` elements, then each `iframe` has its own
+ * [Window] object, which is accessible only to that `iframe`.
+ *
+ * See also:
+ *
+ *   * [Window](https://developer.mozilla.org/en-US/docs/Web/API/window) from MDN.
+ */
 Window get window {
   if (_window != null) {
     return _window;
   }
   _window = _Utils.window();
   return _window;
 }
 
 HtmlDocument _document;
 
+/**
+ * Root node for all content in a web page.
+ */
 HtmlDocument get document {
   if (_document != null) {
     return _document;
   }
   _document = window.document;
   return _document;
 }
 
 
 Element query(String selector) => document.query(selector);
@@ skipping 10 matching lines @@
       _callPortLastResult = json.parse(_getPortSyncEventData(event));
     });
     _callPortInitialized = true;
   }
   assert(_callPortLastResult == null);
   _dispatchEvent('js-sync-message', {'id': id, 'message': message});
   var result = _callPortLastResult;
   _callPortLastResult = null;
   return result;
 }