Don't allow escaping newlines in single line strings.

dart/tests/language/src/StringEscape2NegativeTest.dart

Index: dart/tests/language/src/StringEscape2NegativeTest.dart
diff --git a/dart/tests/language/src/StringEscape2NegativeTest.dart b/dart/tests/language/src/StringEscape2NegativeTest.dart
new file mode 100644
index 0000000000000000000000000000000000000000..2ad04821515175d956ff257726afa061a59de859
--- /dev/null
+++ b/dart/tests/language/src/StringEscape2NegativeTest.dart
@@ -0,0 +1,11 @@
+// Copyright (c) 2012, 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.
+
+// Test that newlines cannot be escaped in source tags.
+
+#source('StringEscape2NegativeTestHelper\
+.dart');
+
+main() {
+}