Add a JSON reporter.

test/runner/browser/compact_reporter_test.dart

 // Copyright (c) 2015, 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.
 
 @TestOn("vm")
 
 import 'package:scheduled_test/descriptor.dart' as d;
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../../io.dart';
 
 void main() {
   useSandbox();
 
   test("prints the platform name when running on multiple platforms", () {
     d.file("test.dart", """
 import 'dart:async';
 
 import 'package:path/path.dart' as p;
 import 'package:test/test.dart';
 
 void main() {
   test("success", () {});
 }
 """).create();
 
     var test = runTest([
-      "-r", "compact",
       "-p", "content-shell",
       "-p", "vm",
       "-j", "1",
       "test.dart"
-    ], compact: true);
+    ], reporter: "compact");
 
     test.stdout.expect(containsInOrder(["[VM]", "[Dartium Content Shell]"]));
 
     test.shouldExit(0);
   });
 }