Add optimized _OneByteString.toLowerCase.

tests/corelib/string_to_lower_case_test.dart

+// 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));
+  var twoByteString = new String.fromCharCodes(

[sra1, 2014/03/25 21:29:13]

This is probably a _OneByteString.
You have to do the toLowerCase before the substring to guarantee the operation
happens on a one byte string.

Maybe you should add an assert that there are two byte characters in the string

  Expect.isTrue(twoByteString.codeUnits.any((u) => u >= 256);

Before you check in, temporarily add a mistake to the table to see that the test
finds the problem.

[Anders Johnsen, 2014/03/25 21:37:48]

Done.

+      new List.generate(512, (i)=> i)).substring(0, 256);
+  Expect.listEquals(oneByteString.toLowerCase(), twoByteString.toLowerCase());

[sra1, 2014/03/25 21:29:13]

Expect.equals.

(This will fail in checked mode since a String is not a List.)

[Anders Johnsen, 2014/03/25 21:37:48]

Done.

+}
+
+void main() {
+  testOneByteSting();
+}