Add some support for the code-point code-unit distinction.

tests/corelib/string_trim_unicode_test.dart

+// 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.
+
+class Range {
+  final int from;
+  final int to;
+  const Range(this.from, this.to);
+}
+
+class StringTrimTest {
+  static testMain() {
+    var spaces = [
+        const Range(9, 13),  // Control characters, not in the Zs category.
+        const Range(32, 32),
+        const Range(0xa0, 0xa0),
+        const Range(0x1680, 0x1680),
+        const Range(0x180e, 0x180e),
+        const Range(0x2000, 0x200a),
+        // LINE SEPARATOR, category Zl and PARAGRAPH SEPARATOR, category Zp.
+        const Range(0x2028, 0x2029),
+        const Range(0x202f, 0x202f),
+        const Range(0x205f, 0x205f),
+        const Range(0x3000, 0x3000),
+        const Range(0xfeff, 0xfeff)];  // Unicode BOM.
+    for (int range in spaces) {
+      for (int i = range.from - 1; i <= range.to + 1; i++) {
+        print("Check $i");
+        if (i >= range.from && i <= range.to) {
+          Expect.equals(
+              new String.fromCharCodes([i, 'f'.charCodeAt(0), i]).trim(), 'f');
+        } else {
+          Expect.isFalse('f' ==
+              new String.fromCharCodes([i, 'f'.charCodeAt(0), i]).trim());
+        }
+      }
+    }
+    // 0x85 NEL Next line is not in the Unicode Zs category and it not special
+    // cased in the ES5 spec either.
+    Expect.isFalse('f' ==
+        new String.fromCharCodes([0x85, 'f'.charCodeAt(0), 0x85]).trim());
+  }
+}
+
+main() {
+  StringTrimTest.testMain();
+}