Added helpful information on all event getters and static members.

tools/dom/templates/html/impl/impl_Window.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.
 
 part of $LIBRARYNAME;
 
 @DocsEditable()
 $if DART2JS
 $(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS native "Window,DOMWindow" {
 $else
@@ skipping 253 matching lines @@
     return new Point(result.x, result.y);
   }
 
   /**
    * Checks whether [convertPointFromNodeToPage] and
    * [convertPointFromPageToNode] are supported on the current platform.
    */
   static bool get supportsPointConversions => _DomPoint.supported;
 $!MEMBERS
 
+  /**
+   * Static factory designed to expose `beforeunload` events to event
+   * handlers that are not necessarily instances of [Window].
+   *
+   * See [EventStreamProvider] for usage information.
+   */
   @DomName('Window.beforeunloadEvent')
-  @DocsEditable()
   static const EventStreamProvider<BeforeUnloadEvent> beforeUnloadEvent =
       const _BeforeUnloadEventStreamProvider('beforeunload');
 
+  /// Stream of `beforeunload` events handled by this [Window].
   @DomName('Window.onbeforeunload')
-  @DocsEditable()
   Stream<Event> get onBeforeUnload => beforeUnloadEvent.forTarget(this);
 
   void moveTo(Point p) {
     _moveTo(p.x, p.y);
   }
 
 $if DART2JS
   int get scrollX => JS('bool', '("scrollX" in #)', this) ? JS('int',
       '#.scrollX', this) : document.documentElement.scrollLeft;
   int get scrollY => JS('bool', '("scrollY" in #)', this) ? JS('int',
@@ skipping 35 matching lines @@
       return wrapped.returnValue;
     });
 
     return controller.stream;
   }
 
   String getEventType(EventTarget target) {
     return _eventType;
   }
 }