Refactor Future constructors.

pkg/scheduled_test/lib/src/scheduled_server/handler.dart

Index: pkg/scheduled_test/lib/src/scheduled_server/handler.dart
diff --git a/pkg/scheduled_test/lib/src/scheduled_server/handler.dart b/pkg/scheduled_test/lib/src/scheduled_server/handler.dart
index 6be6b1c2112970ad695db8fc9c66d038146a1e11..4d6c6b8a4c70fcd6ffb4d94cb18a994820c95f25 100644
--- a/pkg/scheduled_test/lib/src/scheduled_server/handler.dart
+++ b/pkg/scheduled_test/lib/src/scheduled_server/handler.dart
@@ -54,7 +54,7 @@ class Handler {
         // between a test failing while waiting for a handler and a test failing
         // while executing a handler.
         chainToCompleter(schedule(() {
-          return new Future.of(() {
+          return new Future.sync(() {
             if (request.method != method || request.uri.path != path) {
               throw "'${server.description}' expected $method $path, "
                   "but got ${request.method} ${request.uri.path}.";