Add a JSON reporter.

test/io.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.
 
 library test.test.io;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
@@ skipping 76 matching lines @@
 
 /// Returns a [StreamMatcher] that asserts that the stream emits strings
 /// containing each string in [strings] in order.
 ///
 /// This expects each string in [strings] to match a different string in the
 /// stream.
 StreamMatcher containsInOrder(Iterable<String> strings) =>
     inOrder(strings.map((string) => consumeThrough(contains(string))));
 
 /// Runs the test executable with the package root set properly.
-ScheduledProcess runTest(List args, {bool compact: false,
+ScheduledProcess runTest(List args, {String reporter,
     int concurrency, Map<String, String> environment}) {
-  if (concurrency == null) concurrency = 1;
+  reporter ??= "expanded";
+  concurrency ??= 1;
 
   var allArgs = [
     p.absolute(p.join(packageDir, 'bin/test.dart')),
     "--package-root=${p.join(packageDir, 'packages')}",
-    "--concurrency=$concurrency"
-  ];
-
-  if (!compact) allArgs.addAll(["-r", "expanded"]);
-  allArgs.addAll(args);
+    "--concurrency=$concurrency",
+    "--reporter=$reporter"
+  ]..addAll(args);
 
   if (environment == null) environment = {};
   environment.putIfAbsent("_UNITTEST_USE_COLOR", () => "false");
 
   return runDart(allArgs,
       environment: environment,
       description: "dart bin/test.dart");
 }
 
 /// Runs Dart.
@@ skipping 41 matching lines @@
     var match;
     while (match == null) {
       var line = await pub.stdout.next();
       match = _servingRegExp.firstMatch(line);
     }
     _pubServePortCompleter.complete(int.parse(match[1]));
   }, "waiting for pub serve to emit its port number");
 
   return pub;
 }