Try and fix test for windows, by delaying dir delete to file-stream's onDone is called.

tests/standalone/io/file_input_stream_test.dart

Index: tests/standalone/io/file_input_stream_test.dart
diff --git a/tests/standalone/io/file_input_stream_test.dart b/tests/standalone/io/file_input_stream_test.dart
index 5a4adf1911de4a73c25c1a0616c384a07e53e67f..d57c0147b10ce2e66bfae4b20a30adfd99208232 100644
--- a/tests/standalone/io/file_input_stream_test.dart
+++ b/tests/standalone/io/file_input_stream_test.dart
@@ -212,9 +212,10 @@ void testInputStreamBadOffset() {
           streamedBytes += d.length;
         },
         onDone: () {
+          temp.delete(recursive: true);
         },
         onError: (e) {
-          temp.delete(recursive: true).then((_) => keepAlive.close());
+          keepAlive.close();
         });
   }
   test(-1, null);