Add timeout getter to Configuration.

dart/pkg/unittest/lib/src/configuration.dart

Index: dart/pkg/unittest/lib/src/configuration.dart
diff --git a/dart/pkg/unittest/lib/src/configuration.dart b/dart/pkg/unittest/lib/src/configuration.dart
index c9ec1c0718d7f5f26ee39e2f5e3abba8de8d6dd1..1862bf5464ca2a210502cf354acbe411984e26c7 100644
--- a/dart/pkg/unittest/lib/src/configuration.dart
+++ b/dart/pkg/unittest/lib/src/configuration.dart
@@ -28,6 +28,9 @@ abstract class Configuration {
    */
   bool get autoStart => true;
 
+  /// How long a [TestCase] can run before it is considered an error.
+  Duration get timeout => const Duration(seconds: 20);
+
   /**
    * Called as soon as the unittest framework becomes initialized. This is done
    * even before tests are added to the test framework. It might be used to