Remove support for attribute event listeners.

client/samples/sunflower/Sunflower.dart

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #library('sunflower');
 
 #import('dart:dom');
 
 #resource('sunflower.css');
 
 main() {
   new Sunflower();
 }
 
 class Sunflower {
   
   Sunflower() {
     PHI = (Math.sqrt(5) + 1) / 2;
     var doc = window.document;
     
     HTMLCanvasElement canvas = doc.getElementById("canvas");
     xc = yc = MAX_D / 2;
     ctx = canvas.getContext("2d");
     
     HTMLInputElement slider = doc.getElementById("slider");
-    slider.onchange = (Event e) {
+    slider.addEventListener('change', (Event e) {
       seeds = Math.parseInt(slider.value);
       drawFrame();
-    };
+    }, true);
     
     drawFrame();
   }
   
   // Draw the complete figure for the current number of seeds.
   void drawFrame() {
     ctx.clearRect(0, 0, MAX_D, MAX_D);
     for (var i=0; i<seeds; i++) {
       var theta = i * TAU / PHI;
       var r = Math.sqrt(i) * SCALE_FACTOR;
@@ skipping 20 matching lines @@
   num seeds = 0;
 
   static final SEED_RADIUS = 2;
   static final SCALE_FACTOR = 4;
   static final TAU = Math.PI * 2;
   var PHI;
   static final MAX_D = 300;
   static final String ORANGE = "orange";
 
 }