Prefix string literal must be identifier

tests/language/src/Prefix18NegativeTest_1.dart

Index: tests/language/src/Prefix18NegativeTest_1.dart
diff --git a/tests/language/src/Prefix18NegativeTest_1.dart b/tests/language/src/Prefix18NegativeTest_1.dart
new file mode 100644
index 0000000000000000000000000000000000000000..84372ffac287999962431ed5e7da7d3ae0586dc2
--- /dev/null
+++ b/tests/language/src/Prefix18NegativeTest_1.dart
@@ -0,0 +1,11 @@
+// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+//
+// prefix: strings should only contain valid identifiers
+
+#library("Prefix18NegativeTest.dart");
+#import("library1.dart", prefix:"lib1.invalid");
+
+main() {
+}