Fix bug in trim introduced by rewrite.

tests/corelib/string_trim2_test.dart

 // Copyright (c) 2013, 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";
 
 const WHITESPACE = const [
   0x09,
   0x0A,
   0x0B,
@@ skipping 18 matching lines @@
   0x202F,
   0x205F,
   0x3000,
   0x2028,
   0x2029,
   0xFEFF,
 ];
 
 main() {
   for (var ws in WHITESPACE) {
-    Expect.equals("", new String.fromCharCode(ws).trim());
+    var name = ws.toRadixString(16);
+    var c = new String.fromCharCode(ws);
+    Expect.equals("", c.trim(), "$name");
+    Expect.equals("a", ("a" + c).trim(), "a-$name");
+    Expect.equals("a", (c + "a").trim(), "$name-a");
+    Expect.equals("a", (c + c + "a" + c + c).trim(), "$name around");
+    Expect.equals("a" + c + "a", (c + c + "a" + c + "a" + c + c).trim(),
+                  "$name many");
   }
-  Expect.equals("", new String.fromCharCodes(WHITESPACE).trim());
-  for (var ws in WHITESPACE) {
-    var c = new String.fromCharCode(ws);
-    Expect.equals("a", ("a" + c).trim());
-    Expect.equals("a", (c + "a").trim());
-    Expect.equals("a", (c + c + "a" + c + c).trim());
-    Expect.equals("a" + c + "a", (c + c + "a" + c + "a" + c + c).trim());
-  }
+  Expect.equals("", new String.fromCharCodes(WHITESPACE).trim(), "ALL");
 }