Add --additional-compiler-flags option to tweak compilation.

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 194 matching lines @@
               [],
               ''),
           new _TestOptionSpecification(
               'time',
               'Print timing information after running tests',
               ['--time'],
               [],
               false,
               'bool'),
           new _TestOptionSpecification(
+              'additional-compiler-flags',
+              'Additional flags to control test compilation',
+              ['--additional-compiler-flags'],
+              [],
+              ''),
+          new _TestOptionSpecification(
               'dart',
               'Path to dart executable',
               ['--dart'],
               [],
               ''),
           new _TestOptionSpecification(
               'drt',
               'Path to DumpRenderTree executable',
               ['--drt'],
               [],
@@ skipping 402 matching lines @@
         return option;
       }
     }
     print('Unknown test option $name');
     exit(1);
   }
 
 
   List<_TestOptionSpecification> _options;
 }