Support a @Timeout annotation.

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 80f9774eefc82df5a18511c07a3ff6138c2514f3..97d779ab86b24b41a419a5c3b53a9aea44ab1f17 100644
--- a/test/runner/browser/runner_test.dart
+++ b/test/runner/browser/runner_test.dart
@@ -258,6 +258,24 @@ void main() {
     expect(result.stdout, contains("Hello,\nworld!\n"));
     expect(result.exitCode, equals(0));
   });
+
+  test("respects top-level @Timeout declarations", () {
+    new File(p.join(_sandbox, "test.dart")).writeAsStringSync('''
+@Timeout(const Duration(seconds: 0))
+
+import 'dart:async';
+
+import 'package:test/test.dart';
+
+void main() {
+  test("timeout", () {});
+}
+''');
+
+    var result = _runUnittest(["-p", "chrome", "test.dart"]);
+    expect(result.stdout, contains("Test timed out after 0 seconds."));
+    expect(result.stdout, contains("-1: Some tests failed."));
+  });
 }
 
 ProcessResult _runUnittest(List<String> args) =>