Converting tests over to using event streams.

tests/html/url_test.dart

Index: tests/html/url_test.dart
diff --git a/tests/html/url_test.dart b/tests/html/url_test.dart
index c52b7c6d885ec10f8f93eba1462f743ca50c7d30..f332b30e75e383eec2b61b0bda56cdb1901f59d3 100644
--- a/tests/html/url_test.dart
+++ b/tests/html/url_test.dart
@@ -41,10 +41,10 @@ main() {
       expect(url, startsWith('blob:'));
 
       var img = new ImageElement();
-      img.on.load.add(expectAsync1((_) {
+      img.onLoad.listen(expectAsync1((_) {
         expect(img.complete, true);
       }));
-      img.on.error.add((_) {
+      img.onError.listen((_) {
         guardAsync(() {
           expect(true, isFalse, reason: 'URL failed to load.');
         });
@@ -60,9 +60,9 @@ main() {
 
       var img = new ImageElement();
       // Image should fail to load since the URL was revoked.
-      img.on.error.add(expectAsync1((_) {
+      img.onError.listen(expectAsync1((_) {
       }));
-      img.on.load.add((_) {
+      img.onLoad.listen((_) {
         guardAsync(() {
           expect(true, isFalse, reason: 'URL should not have loaded.');
         });