Add 'diff' option to progress.

tools/testing/dart/test_options.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 test_options_parser;
 
 import "dart:io";
 import "dart:math";
 import "drt_updater.dart";
 import "test_suite.dart";
@@ skipping 138 matching lines @@
               'Timeout in seconds',
               ['-t', '--timeout'],
               [],
               -1,
               'int'),
           new _TestOptionSpecification(
               'progress',
               'Progress indication mode',
               ['-p', '--progress'],
               ['compact', 'color', 'line', 'verbose',
-               'silent', 'status', 'buildbot'],
+               'silent', 'status', 'buildbot', 'diff'],
               'compact'),
           new _TestOptionSpecification(
               'step_name',
               'Step name for use by -pbuildbot',
               ['--step_name'],
               [],
               null),
           new _TestOptionSpecification(
               'report',
               'Print a summary report of the number of tests, by expectation',
@@ skipping 514 matching lines @@
         return option;
       }
     }
     print('Unknown test option $name');
     exit(1);
   }
 
 
   List<_TestOptionSpecification> _options;
 }