Add basic support for a configuration file.

test/runner/runner_test.dart

 // Copyright (c) 2015, 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.
 
 @TestOn("vm")
 
 import 'dart:io';
 import 'dart:math' as math;
 
 import 'package:scheduled_test/descriptor.dart' as d;
@@ skipping 42 matching lines @@
 
 -N, --plain-name               A plain-text substring of the name of the test to run.
 -t, --tags                     Run only tests with all of the specified tags.
 -x, --exclude-tags             Don't run tests with any of the specified tags.
 
 ======== Running Tests
 -p, --platform                 The platform(s) on which to run the tests.
                                $_browsers
 
 -j, --concurrency=<threads>    The number of concurrent test suites run.
-                               (defaults to $_defaultConcurrency)
+                               (defaults to "$_defaultConcurrency")
 
     --pub-serve=<port>         The port of a pub serve instance serving "test/".
     --timeout                  The default test timeout. For example: 15s, 2x, none
-                               (defaults to 30s)
+                               (defaults to "30s")
 
     --pause-after-load         Pauses for debugging before any tests execute.
                                Implies --concurrency=1 and --timeout=none.
                                Currently only supported for browser tests.
 
 ======== Output
 -r, --reporter                 The runner used to print test results.
 
           [compact]            A single line, updated continuously.
           [expanded]           A separate line for each update.
@@ skipping 584 matching lines @@
         d.file("test.dart", _success).create();
 
         var test = runTest(["--plain-name", "no match", "test.dart"]);
         test.stderr.expect(
             consumeThrough(contains('No tests match "no match".')));
         test.shouldExit(exit_codes.data);
       });
     });
   });
 }