Adding API to remove send ports from Window.

sdk/lib/html/dart2js/html_dart2js.dart

Index: sdk/lib/html/dart2js/html_dart2js.dart
diff --git a/sdk/lib/html/dart2js/html_dart2js.dart b/sdk/lib/html/dart2js/html_dart2js.dart
index 0cf52e56c103e954a9d1f4a5373eaf4cfa460e19..1570ab1f8bb87bf768118ad84d65d433e8e81074 100644
--- a/sdk/lib/html/dart2js/html_dart2js.dart
+++ b/sdk/lib/html/dart2js/html_dart2js.dart
@@ -23996,6 +23996,15 @@ class Window extends EventTarget implements WindowBase, WindowTimers native "Win
   }
 
   /**
+   * 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.
    *
@@ -25004,9 +25013,9 @@ class Window extends EventTarget implements WindowBase, WindowTimers native "Win
     $dom_moveTo(p.x, p.y);
   }
 
-  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;
 }