Add synchronous directory listing to dart:io Directory.

tests/standalone/io/directory_fuzz_test.dart

Index: tests/standalone/io/directory_fuzz_test.dart
diff --git a/tests/standalone/io/directory_fuzz_test.dart b/tests/standalone/io/directory_fuzz_test.dart
index 3d982e6459e777eb2bb2ab36cf04104776446a4f..dd6fe0d14736046a28ed3f434d3e7f69b96a4e80 100644
--- a/tests/standalone/io/directory_fuzz_test.dart
+++ b/tests/standalone/io/directory_fuzz_test.dart
@@ -17,6 +17,7 @@ fuzzSyncMethods() {
       doItSync(d.existsSync);
       doItSync(d.createSync);
       doItSync(d.deleteSync);
+      doItSync(d.listSync);
       doItSync(() {
         d.createTempSync().deleteSync();
       });
@@ -27,6 +28,7 @@ fuzzSyncMethods() {
       });
       typeMapping.forEach((k2, v2) {
         doItSync(() => d.renameSync(v2));
+        doItSync(() => d.listSync(recursive: v2));
         doItSync(() => d.list(recursive: v2).onError = (e) => null);
       });
     });