Add optimized _OneByteString.toLowerCase.

tests/corelib/string_to_lower_case_test.dart

Index: tests/corelib/string_to_lower_case_test.dart
diff --git a/tests/corelib/string_to_lower_case_test.dart b/tests/corelib/string_to_lower_case_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..1af1dd53ded6d46a54498391ac3a64bab4471ed0
--- /dev/null
+++ b/tests/corelib/string_to_lower_case_test.dart
@@ -0,0 +1,19 @@
+// Copyright (c) 2014, 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.
+
+import "package:expect/expect.dart";
+
+void testOneByteSting() {
+  // Compare one-byte-string toLowerCase with a two-byte-string toLowerCase.
+  var oneByteString = new String.fromCharCodes(
+      new List.generate(256, (i) => i)).toLowerCase();
+  var twoByteString = new String.fromCharCodes(
+      new List.generate(512, (i) => i)).toLowerCase();
+  Expect.isTrue(twoByteString.codeUnits.any((u) => u >= 256));
+  Expect.equals(oneByteString, twoByteString.substring(0, 256));
+}
+
+void main() {
+  testOneByteSting();
+}