Update almost all tests (except co19) to use the new try-catch syntax.

tests/html/exceptions_test.dart

Index: tests/html/exceptions_test.dart
diff --git a/tests/html/exceptions_test.dart b/tests/html/exceptions_test.dart
index 8e7250f04550b265dead326a6c1430dfb0d1ee3d..984a3d0e00b5c3896ba318821904320f5c39f5b3 100644
--- a/tests/html/exceptions_test.dart
+++ b/tests/html/exceptions_test.dart
@@ -8,7 +8,7 @@ main() {
   test('DOMException', () {
     try {
       window.webkitNotifications.createNotification('', '', '');
-    } catch (DOMException e) {
+    } on DOMException catch (e) {
       Expect.equals(DOMException.SECURITY_ERR, e.code);
       Expect.equals('SECURITY_ERR', e.name);
       Expect.equals('SECURITY_ERR: DOM Exception 18', e.message);
@@ -19,7 +19,7 @@ main() {
     // Intentionally do not initialize it!
     try {
       document.$dom_dispatchEvent(event);
-    } catch (EventException e) {
+    } on EventException catch (e) {
       Expect.equals(EventException.UNSPECIFIED_EVENT_TYPE_ERR, e.code);
       Expect.equals('UNSPECIFIED_EVENT_TYPE_ERR', e.name);
       Expect.equals('UNSPECIFIED_EVENT_TYPE_ERR: DOM Events Exception 0', e.message);