Split up some slow pub tests and mark some scheduled_test tests as slow.

pkg/scheduled_test/test/scheduled_server_test.dart

Index: pkg/scheduled_test/test/scheduled_server_test.dart
diff --git a/pkg/scheduled_test/test/scheduled_server_test.dart b/pkg/scheduled_test/test/scheduled_server_test.dart
index b34765c6f22e3754b787db3802e7d552bcf767d8..5cbf0a7f38ec788bffa8e553b60df2f9aa7771cd 100644
--- a/pkg/scheduled_test/test/scheduled_server_test.dart
+++ b/pkg/scheduled_test/test/scheduled_server_test.dart
@@ -17,8 +17,8 @@ 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): Only increase the timeout length for the Windows bots once
+    // we track down the cause of >5s HTTP requests on the Linux and Mac bots.
     currentSchedule.timeout = new Duration(seconds: 10);
   });