Adding API to remove send ports from Window.

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;
 
 $if DART2JS
 $(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS native "Window,DOMWindow" {
 $else
 $(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
@@ skipping 30 matching lines @@
    * port may be retrieved by any isolate (or JavaScript script)
    * running in this window.
    */
   void registerPort(String name, var port) {
     var serialized = _serialize(port);
     document.documentElement.attributes['dart-port:$name'] =
         json.stringify(serialized);
   }
 
   /**
+   * Deregister a [port] on this window under the given [name].  This
+   * port may be retrieved by any isolate (or JavaScript script)
+   * running in this window.
+   */
+  void deregisterPort(String name) {
+    document.documentElement.attributes.remove('dart-port:$name');
+  }
+
+  /**
    * Returns a Future that completes just before the window is about to
    * repaint so the user can draw an animation frame.
    *
    * If you need to later cancel this animation, use [requestAnimationFrame]
    * instead.
    *
    * The [Future] completes to a timestamp that represents a floating
    * point value of the number of milliseconds that have elapsed since the page
    * started to load (which is also the timestamp at this call to
    * animationFrame).
@@ skipping 215 matching lines @@
 
   @DomName('Window.onbeforeunload')
   @DocsEditable()
   Stream<Event> get onBeforeUnload => beforeUnloadEvent.forTarget(this);
 
   void moveTo(Point p) {
     $dom_moveTo(p.x, p.y);
   }
 
 $if DART2JS
-  int get scrollX => JS('bool', '("scrollX" in #)', this) ? JS('int', 
+  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', 
+  int get scrollY => JS('bool', '("scrollY" in #)', this) ? JS('int',
       '#.scrollY', this) : document.documentElement.scrollTop;
 $endif
 }
 
 /**
  * Event object that is fired before the window is closed.
  *
  * The standard window close behavior can be prevented by setting the
  * [returnValue]. This will display a dialog to the user confirming that they
  * want to close the page.
@@ skipping 40 matching lines @@
       return wrapped.returnValue;
     });
 
     return controller.stream;
   }
 
   String getEventType(EventTarget target) {
     return _eventType;
   }
 }