Implementation of resize event.

class ResizeLayoutPanelImplStandard extends ResizeLayoutPanelImpl implements EventListener {
 /**
  * Chrome does not fire an onresize event if the dimensions are too small to
  * render a scrollbar.
  */
 static final String _MIN_SIZE = "20px";

 dart_html.Element _collapsible;
 dart_html.Element _collapsibleInner;
 dart_html.Element _expandable;
 dart_html.Element _expandableInner;
 int _lastOffsetHeight = -1;
 int _lastOffsetWidth = -1;
 bool _resettingScrollables = false;

 
 void init(dart_html.Element elem, ResizeDelegate delegate) {
   super.init(elem, delegate);

   /*
    * Set the minimum dimensions to ensure that scrollbars are rendered and
    * fire onscroll events.
    */
   elem.style.minWidth = _MIN_SIZE;
   elem.style.minHeight = _MIN_SIZE;

   /*
    * Detect expansion. In order to detect an increase in the size of the
    * widget, we create an absolutely positioned, scrollable div with
    * height=width=100%. We then add an inner div that has fixed height and
    * width equal to 100% (converted to pixels) and set scrollLeft/scrollTop
    * to their maximum. When the outer div expands, scrollLeft/scrollTop
    * automatically becomes a smaller number and trigger an onscroll event.
    */
   _expandable = new dart_html.DivElement();
   _expandable.style.visibility = Visibility.HIDDEN.value;
   _expandable.style.position = Position.ABSOLUTE.value;
   _expandable.style.height = "100" + Unit.PCT.value;
   _expandable.style.width = "100" + Unit.PCT.value;
   _expandable.style.overflow = Overflow.SCROLL.value;
   elem.append(_expandable);
   _expandableInner = new dart_html.DivElement();
   _expandable.append(_expandableInner);
   Dom.sinkEvents(_expandable, IEvent.ONSCROLL);

   /*
    * Detect collapse. In order to detect a decrease in the size of the
    * widget, we create an absolutely positioned, scrollable div with
    * height=width=100%. We then add an inner div that has height=width=200%
    * and max out the scrollTop/scrollLeft. When the height or width
    * decreases, the inner div loses 2px for every 1px that the scrollable
    * div loses, so the scrollTop/scrollLeft decrease and we get an onscroll
    * event.
    */
   _collapsible = new dart_html.DivElement();
   _collapsible.style.visibility = Visibility.HIDDEN.value;
   _collapsible.style.position = Position.ABSOLUTE.value;
   _collapsible.style.height = "100" + Unit.PCT.value;
   _collapsible.style.width = "100" + Unit.PCT.value;
   _collapsible.style.overflow = Overflow.SCROLL.value;
   elem.append(_collapsible);
   _collapsibleInner = new dart_html.DivElement();
   _collapsibleInner.style.width = "200" + Unit.PCT.value;
   _collapsibleInner.style.height = "200" + Unit.PCT.value;
   _collapsible.append(_collapsibleInner);
   Dom.sinkEvents(_collapsible, IEvent.ONSCROLL);
 }

 
 void onAttach() {
   super.onAttach();
   Dom.setEventListener(_expandable, this);
   Dom.setEventListener(_collapsible, this);

   /*
    * Update the scrollables in a deferred command so the browser calculates
    * the offsetHeight/Width correctly.
    */
   Scheduler.get().scheduleDeferred(new _ScheduledCommand(this));
 }

 void onBrowserEvent(dart_html.Event event) {
   if (!_resettingScrollables && IEvent.ONSCROLL == Dom.eventGetType(event)) {
     dart_html.EventTarget eventTarget = event.target;
     if (eventTarget is! dart_html.Element) {
       return;
     }
     dart_html.Element target = eventTarget as dart_html.Element;
     if (target == _collapsible || target == _expandable) {
       handleResize();
     }
   }
 }

 
 void onDetach() {
   super.onDetach();
   Dom.setEventListener(_expandable, null);
   Dom.setEventListener(_collapsible, null);
   _lastOffsetHeight = -1;
   _lastOffsetWidth = -1;
 }

 
 void handleResize() {
   if (_resetScrollables()) {
     super.handleResize();
   }
 }

 /**
  * Reset the positions of the scrollable elements.
  * 
  * @return true if the size changed, false if not
  */
 bool _resetScrollables() {
   /*
    * Older versions of safari trigger a synchronous scroll event when we
    * update scrollTop/scrollLeft, so we set a bool to ignore that event.
    */
   if (_resettingScrollables) {
     return false;
   }
   _resettingScrollables = true;

   /*
    * Reset expandable element. Scrollbars are not rendered if the div is too
    * small, so we need to set the dimensions of the inner div to a value
    * greater than the offsetWidth/Height.
    */
   int offsetHeight = parent.offset.height;
   int offsetWidth = parent.offset.width;
   int height = offsetHeight + 100;
   int width = offsetWidth + 100;
   _expandableInner.style.height = height.toString() + Unit.PX.value;
   _expandableInner.style.width = width.toString() + Unit.PX.value;
   _expandable.scrollTop = height;
   _expandable.scrollLeft = width;

   // Reset collapsible element.
   _collapsible.scrollTop = _collapsible.scrollHeight + 100;
   _collapsible.scrollLeft = _collapsible.scrollWidth + 100;

   if (_lastOffsetHeight != offsetHeight || _lastOffsetWidth != offsetWidth) {
     _lastOffsetHeight = offsetHeight;
     _lastOffsetWidth = offsetWidth;
     _resettingScrollables = false;
     return true;
   }
   _resettingScrollables = false;
   return false;
 }
}