Change ImageElement to use onLoad.listen instead of on.load and

samples/openglui/src/openglui_canvas_tests.dart

 // Copyright (c) 2012, 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.
 //
 // Canvas API tests. Some of these are adapted from:
 //
 // http://www.html5canvastutorials.com/
 
 library openglui_canvas_tests;
 
@@ skipping 482 matching lines @@
   ctx.setLineDash([]);
   ctx.strokeStyle = "#0000FF";
   ctx.strokeStyle = "rgba(128,128,128, 0.5)";
   ctx.strokeRect(width / 5, height / 10, width / 2, height / 8);
   log("Width = $width");
 }
 
 void loadImage() {
   initTest("Image loading");
   var imageObj = new ImageElement();
-  // TODO(Gram): Change gl.dart to handle to onLoad.listen.
-  imageObj.on.load.add((e) {
-    ctx.drawImage(e, 69, 50);
+  var sub;
+  sub = imageObj.onLoad.listen((e) {
+    ctx.drawImage(e.target, 69, 50);
+    sub.cancel();
   });
   imageObj.src = 'chrome.png';
 }
 
 void clip() {
   initTest("Clipping");
   var x = width / 2;
   var y = height / 2;
   var radius = height / 4;
   var offset = 2 * radius / 3;
@@ skipping 218 matching lines @@
     case 23:
       var rayTracer = new RayTracer();
       rayTracer.render(defaultScene(), ctx, width, height);
       break;
     default:
       if (testnum < 0) {
         testnum = 23;
       } else {
         testnum = 0;
       }
-      update();
-      break;
+      return;
   }
   isDirty = false;
 }
 
 // Raytracer adapted from https://gist.github.com/mythz/3817303.
 
 Scene defaultScene() =>
    new Scene(
       [new Plane(new Vector(0.0, 1.0, 0.0), 0.0, Surfaces.checkerboard),
        new Sphere(new Vector(0.0, 1.0, -0.25), 1.0, Surfaces.shiny),
@@ skipping 243 matching lines @@
       for (int x = 0; x < screenWidth; x++) {
         var color = _traceRay(new Ray(scene.camera.pos,
             getPoint(x, y, scene.camera) ), scene, 0);
         ctx.fillStyle = Color.toDrawingRGB(color);
         ctx.fillRect(x, y, x + 1, y + 1);
       }
     }
   }
 }