Add firefox support.

test/runner/browser/runner_test.dart

Index: test/runner/browser/runner_test.dart
diff --git a/test/runner/browser/runner_test.dart b/test/runner/browser/runner_test.dart
index aea05886d3756e828653b590adb81018a3dcd6fa..74b3a470d6846fb6d236699532a27539a8e527cf 100644
--- a/test/runner/browser/runner_test.dart
+++ b/test/runner/browser/runner_test.dart
@@ -96,12 +96,18 @@ void main() {
   });
 
   group("runs successful tests", () {
-    test("on the browser only", () {
+    test("on Chrome", () {
       new File(p.join(_sandbox, "test.dart")).writeAsStringSync(_success);
       var result = _runUnittest(["-p", "chrome", "test.dart"]);
       expect(result.exitCode, equals(0));
     });
 
+    test("on Firefox", () {
+      new File(p.join(_sandbox, "test.dart")).writeAsStringSync(_success);
+      var result = _runUnittest(["-p", "firefox", "test.dart"]);
+      expect(result.exitCode, equals(0));
+    });
+
     test("on the browser and the VM", () {
       new File(p.join(_sandbox, "test.dart")).writeAsStringSync(_success);
       var result = _runUnittest(["-p", "chrome", "-p", "vm", "test.dart"]);
@@ -110,7 +116,7 @@ void main() {
   });
 
   group("runs failing tests", () {
-    test("on the browser only", () {
+    test("on Chrome", () {
       new File(p.join(_sandbox, "test.dart")).writeAsStringSync("""
 import 'dart:async';
 
@@ -124,6 +130,20 @@ void main() {
       expect(result.exitCode, equals(1));
     });
 
+    test("on Firefox", () {
+      new File(p.join(_sandbox, "test.dart")).writeAsStringSync("""
+import 'dart:async';
+
+import 'package:test/test.dart';
+
+void main() {
+  test("failure", () => throw new TestFailure("oh no"));
+}
+""");
+      var result = _runUnittest(["-p", "firefox", "test.dart"]);
+      expect(result.exitCode, equals(1));
+    });
+
     test("that fail only on the browser", () {
       new File(p.join(_sandbox, "test.dart")).writeAsStringSync("""
 import 'dart:async';