Add Capability class.

sdk/lib/isolate/isolate.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.
 
 /**
  * Concurrent programming using _isolates_:
  * independent workers that are similar to threads
  * but don't share memory,
  * communicating only via messages.
  *
  * See also:
  * [dart:isolate - Concurrency with Isolates](https://www.dartlang.org/docs/dart-up-and-running/contents/ch03.html#ch03-dartisolate---concurrency-with-isolates)
  * in the library tour.
  */
 library dart.isolate;
 
 import "dart:async";
 
+part "capability.dart";
+
 /**
  * Thrown when an isolate cannot be created.
  */
 class IsolateSpawnException implements Exception {
   // TODO(floitsch): clean up spawn exception.
   const IsolateSpawnException(String this._s);
   String toString() => "IsolateSpawnException: '$_s'";
   final String _s;
 }
 
@@ skipping 203 matching lines @@
   const _IsolateUnhandledException(this.message, this.source, this.stackTrace);
 
   String toString() {
     return 'IsolateUnhandledException: exception while handling message: '
         '${message} \n  '
         '${source.toString().replaceAll("\n", "\n  ")}\n'
         'original stack trace:\n  '
         '${stackTrace.toString().replaceAll("\n","\n  ")}';
   }
 }