Fix widget.dart to work with the latest web_ui library. Specifically, query selectors need to use "…

lib/components/carousel.dart

 import 'dart:async';
 import 'dart:html';
 import 'package:web_ui/web_ui.dart';
 import 'package:bot/bot.dart';
 import 'package:widget/effects.dart';
 import 'package:widget/widget.dart';
 
 // TODO: option to enable/disable wrapping. Disable buttons if the end is hit...
 
 /**
  * [Carousel] allows moving back and forth through a set of child elements.
  *
  * It is based on a [similar component](http://twitter.github.com/bootstrap/javascript.html#carousel)
  * in Bootstrap.
  *
  * [Carousel] leverages the [Swap] component to render the transition between items.
  */
 class Carousel extends WebComponent {
   final ShowHideEffect _fromTheLeft = new SlideEffect(xStart: HorizontalAlignment.LEFT);
   final ShowHideEffect _fromTheRight = new SlideEffect(xStart: HorizontalAlignment.RIGHT);
 
   static const _duration = 2000;
 
   Future<bool> next() => _moveDelta(true);
 
   Future<bool> previous() => _moveDelta(false);
 
-  SwapComponent get _swap => this.query('x-carousel > .carousel > x-swap').xtag;
+  SwapComponent get _swap =>
+      this.query('[is=x-carousel] > .carousel > [is=x-swap]').xtag;
 
   Future<bool> _moveDelta(bool doNext) {
     final swap = _swap;
     assert(swap != null);
-    if(swap.items.length == 0) {
-      return new Future.immediate(false);
+    if (swap.items.length == 0) {
+      return new Future.value(false);
     }
 
     assert(doNext != null);
     final delta = doNext ? 1 : -1;
 
     ShowHideEffect showEffect, hideEffect;
-    if(doNext) {
+    if (doNext) {
       showEffect = _fromTheRight;
       hideEffect = _fromTheLeft;
     } else {
       showEffect = _fromTheLeft;
       hideEffect = _fromTheRight;
     }
 
     final activeIndex = _swap.activeItemIndex;
 
     final newIndex = (activeIndex + delta) % _swap.items.length;
 
-    return _swap.showItemAtIndex(newIndex, effect: showEffect, hideEffect: hideEffect, duration: _duration);
+    return _swap.showItemAtIndex(newIndex, effect: showEffect,
+        hideEffect: hideEffect, duration: _duration);
   }
 }