Getting html_dart2js and html_dartium a bit more in sync.

tools/dom/src/dartium_KeyEvent.dart

 /**
  * A custom KeyboardEvent that attempts to eliminate cross-browser
  * inconsistencies, and also provide both keyCode and charCode information
  * for all key events (when such information can be determined).
  *
  * KeyEvent tries to provide a higher level, more polished keyboard event
  * information on top of the "raw" [KeyboardEvent].
  *
  * This class is very much a work in progress, and we'd love to get information
  * on how we can make this class work with as many international keyboards as
@@ skipping 48 matching lines @@
     new _KeyboardEventHandler('keydown');
   /** Accessor to provide a stream of KeyEvents on the desired target. */
   static EventStreamProvider<KeyEvent> keyUpEvent =
     new _KeyboardEventHandler('keyup');
   /** Accessor to provide a stream of KeyEvents on the desired target. */
   static EventStreamProvider<KeyEvent> keyPressEvent =
     new _KeyboardEventHandler('keypress');
 
   /** True if the altGraphKey is pressed during this event. */
   bool get altGraphKey => _parent.altGraphKey;
+  /** Accessor to the clipboardData available for this event. */
+  DataTransfer get clipboardData => _parent.clipboardData;
   /** True if the ctrl key is pressed during this event. */
   bool get ctrlKey => _parent.ctrlKey;
   int get detail => _parent.detail;
   /**
    * Accessor to the part of the keyboard that the key was pressed from (one of
    * KeyLocation.STANDARD, KeyLocation.RIGHT, KeyLocation.LEFT,
    * KeyLocation.NUMPAD, KeyLocation.MOBILE, KeyLocation.JOYSTICK).
    */
   int get keyLocation => _parent.keyLocation;
   Point get layer => _parent.layer;
@@ skipping 15 matching lines @@
     throw new UnsupportedError("keyIdentifier is unsupported.");
   }
   void $dom_initKeyboardEvent(String type, bool canBubble, bool cancelable,
       Window view, String keyIdentifier, int keyLocation, bool ctrlKey,
       bool altKey, bool shiftKey, bool metaKey,
       bool altGraphKey) {
     throw new UnsupportedError(
         "Cannot initialize a KeyboardEvent from a KeyEvent.");
   }
 }