Don't allow escaping newlines in single line strings.

dart/tests/language/src/StringEscape4NegativeTest.dart

Index: dart/tests/language/src/StringEscape4NegativeTest.dart
diff --git a/dart/tests/language/src/StringEscape4NegativeTest.dart b/dart/tests/language/src/StringEscape4NegativeTest.dart
new file mode 100644
index 0000000000000000000000000000000000000000..d12cdd209e7c3ea0e36b86f4a0d6b4d9583a0ce1
--- /dev/null
+++ b/dart/tests/language/src/StringEscape4NegativeTest.dart
@@ -0,0 +1,10 @@
+// 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 strings.
+
+main() {
+  print('Hello, World!\
+');
+}