Allowing Window.onBeforeUnload event to work properly.

tools/dom/src/dart2js_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
  * possible. Bugs welcome!
  */
-class KeyEvent implements KeyboardEvent {
+class KeyEvent extends _WrappedEvent implements KeyboardEvent {
   /** The parent KeyboardEvent that this KeyEvent is wrapping and "fixing". */
   KeyboardEvent _parent;
 
   /** The "fixed" value of whether the alt key is being pressed. */
   bool _shadowAltKey;
 
   /** Caculated value of what the estimated charCode is for this event. */
   int _shadowCharCode;
 
   /** Caculated value of what the estimated keyCode is for this event. */
@@ skipping 14 matching lines @@
   /** Accessor to the underlying keyCode value is the parent event. */
   int get _realKeyCode => JS('int', '#.keyCode', _parent);
 
   /** Accessor to the underlying charCode value is the parent event. */
   int get _realCharCode => JS('int', '#.charCode', _parent);
 
   /** Accessor to the underlying altKey value is the parent event. */
   bool get _realAltKey => JS('int', '#.altKey', _parent);
 
   /** Construct a KeyEvent with [parent] as the event we're emulating. */
-  KeyEvent(KeyboardEvent parent) {
+  KeyEvent(KeyboardEvent parent): super(parent) {
     _parent = parent;
     _shadowAltKey = _realAltKey;
     _shadowCharCode = _realCharCode;
     _shadowKeyCode = _realKeyCode;
   }
 
   // TODO(efortuna): If KeyEvent is sufficiently successful that we want to make
   // it the default keyboard event handling, move these methods over to Element.
   /** Accessor to provide a stream of KeyEvents on the desired target. */
   static EventStreamProvider<KeyEvent> keyDownEvent =
     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;
-  bool get bubbles => _parent.bubbles;
-  /** True if this event can be cancelled. */
-  bool get cancelable => _parent.cancelable;
-  bool get cancelBubble => _parent.cancelBubble;
-  void set cancelBubble(bool cancel) {
-    _parent.cancelBubble = cancel;
-  }
   /** 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;
-  /** Accessor to the target this event is listening to for changes. */
-  EventTarget get currentTarget => _parent.currentTarget;
-  bool get defaultPrevented => _parent.defaultPrevented;
   int get detail => _parent.detail;
-  int get eventPhase => _parent.eventPhase;
   /**
    * 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;
   /** True if the Meta (or Mac command) key is pressed during this event. */
   bool get metaKey => _parent.metaKey;
   Point get page => _parent.page;
-  bool get returnValue => _parent.returnValue;
-  void set returnValue(bool value) {
-    _parent.returnValue = value;
-  }
   /** True if the shift key was pressed during this event. */
   bool get shiftKey => _parent.shiftKey;
-  int get timeStamp => _parent.timeStamp;
-  /**
-   * The type of key event that occurred. One of "keydown", "keyup", or
-   * "keypress".
-   */
-  String get type => _parent.type;
   Window get view => _parent.view;
-  void preventDefault() => _parent.preventDefault();
-  void stopImmediatePropagation() => _parent.stopImmediatePropagation();
-  void stopPropagation() => _parent.stopPropagation();
   void $dom_initUIEvent(String type, bool canBubble, bool cancelable,
       Window view, int detail) {
     throw new UnsupportedError("Cannot initialize a UI Event from a KeyEvent.");
   }
-  void $dom_initEvent(String eventTypeArg, bool canBubbleArg,
-      bool cancelableArg) {
-    throw new UnsupportedError("Cannot initialize an Event from a KeyEvent.");
-  }
   String get _shadowKeyIdentifier => JS('String', '#.keyIdentifier', _parent);
 
   int get $dom_charCode => charCode;
   int get $dom_keyCode => keyCode;
-  EventTarget get target => _parent.target;
   String get $dom_keyIdentifier {
     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.");
   }
 }