Update unittest to new package layout.

pkg/args/test/args_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.
 
 #library('args_test');
 
-#import('../../unittest/unittest.dart');
-
-// TODO(rnystrom): Use "package:" URL here when test.dart can handle pub.
+// TODO(rnystrom): Use "package:" URL (#4968).
+#import('../../unittest/lib/unittest.dart');
 #import('../lib/args.dart');
 
 main() {
   group('ArgParser.addFlag()', () {
     test('throws IllegalArgumentException if the flag already exists', () {
       var parser = new ArgParser();
       parser.addFlag('foo');
       throwsIllegalArg(() => parser.addFlag('foo'));
     });
 
@@ skipping 639 matching lines @@
         throw new IllegalArgumentException(
             'Line "$line" does not have enough indentation.');
       }
 
       lines[i] = line.substring(indent);
     }
   }
 
   return Strings.join(lines, '\n');
 }