Changed interfaces to abstract classes where possible in {lib,samples,pkg}

lib/isolate/base.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.
 
 class IsolateSpawnException implements Exception {
   const IsolateSpawnException(String this._s);
   String toString() => "IsolateSpawnException: '$_s'";
   final String _s;
 }
 
@@ skipping 32 matching lines @@
  */
 external SendPort spawnUri(String uri);
 
 /**
  * [SendPort]s are created from [ReceivePort]s. Any message sent through
  * a [SendPort] is delivered to its respective [ReceivePort]. There might be
  * many [SendPort]s for the same [ReceivePort].
  *
  * [SendPort]s can be transmitted to other isolates.
  */
-interface SendPort extends Hashable {
+abstract class SendPort implements Hashable {
 
   /**
    * Sends an asynchronous [message] to this send port. The message is copied to
    * the receiving isolate. If specified, the [replyTo] port will be provided to
    * the receiver to facilitate exchanging sequences of messages.
    *
    * The content of [message] can be: primitive values (null, num, bool, double,
    * String), instances of [SendPort], and lists and maps whose elements are any
    * of these. List and maps are also allowed to be cyclic.
    *
@@ skipping 66 matching lines @@
 
   /**
    * Creates a new send port that sends to this receive port. It is legal to
    * create several [SendPort]s from the same [ReceivePort].
    */
   SendPort toSendPort();
 
 }
 
 // TODO(kasperl): Make this hashable and document it.
-interface SendPortSync {
+abstract class SendPortSync {
 
   callSync(var message);
 
 }
 
 class _ReceivePortFactory {
   external factory ReceivePort();
 }