Prefix string literal must be identifier

tests/language/src/Prefix18NegativeTest_3.dart

Index: tests/language/src/Prefix18NegativeTest_3.dart
diff --git a/tests/language/src/Prefix18NegativeTest_3.dart b/tests/language/src/Prefix18NegativeTest_3.dart
new file mode 100644
index 0000000000000000000000000000000000000000..3008884e909825c5ba26ffce453f3105337f8961
--- /dev/null
+++ b/tests/language/src/Prefix18NegativeTest_3.dart
@@ -0,0 +1,12 @@
+// 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");
+
+main() {
+}
+