Mark scheduled_server_test as flaky and increase the timeout on the other scheduled tests.

pkg/scheduled_test/test/scheduled_test_test.dart

Index: pkg/scheduled_test/test/scheduled_test_test.dart
diff --git a/pkg/scheduled_test/test/scheduled_test_test.dart b/pkg/scheduled_test/test/scheduled_test_test.dart
index b1c0acb985426cbd9c1fa24c57996ee0b6ca496b..13fea65ca38b92b9c1661c06bd07dff7931aca67 100644
--- a/pkg/scheduled_test/test/scheduled_test_test.dart
+++ b/pkg/scheduled_test/test/scheduled_test_test.dart
@@ -15,8 +15,9 @@ import 'utils.dart';
 
 void main() {
   metaSetUp(() {
-    // The windows bots are very slow, so we increase the default timeout.
-    if (Platform.operatingSystem != "windows") return;
+    // TODO(nweiz): We used to only increase the timeout to 10s for the Windows
+    // bots, but the Linux and Mac bots have started taking upwards of 5s when
+    // running pumpEventQueue, so we're increasing the timeout across the board.
     currentSchedule.timeout = new Duration(seconds: 10);
   });