Remove obsolete TODOs from tests.

tests/corelib/string_test.dart

 // Copyright (c) 2011, 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";
 
-// TODO(ngeoffray): test String methods with null arguments.
 class StringTest {
 
   static testMain() {
     testOutOfRange();
     testIllegalArgument();
     testConcat();
     testIndex();
     testCodeUnitAt();
     testEquals();
     testEndsWith();
@@ skipping 372 matching lines @@
 
 void testStringLength(int length, String str) {
   Expect.equals(length, str.length);
   (length == 0 ? Expect.isTrue : Expect.isFalse)(str.isEmpty);
   (length != 0 ? Expect.isTrue : Expect.isFalse)(str.isNotEmpty);
 }
 
 main() {
   StringTest.testMain();
 }