isolates refactor: this change introduces 'dart:isolate' as a library. This is a

tests/isolate/src/ConstructorTest.dart

 // Copyright (c) 2011, 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("ConstructorTest");
+#import("dart:isolate");
 #import("TestFramework.dart");
 
 class ConstructorTest extends Isolate {
   final int field;
   ConstructorTest() : super(), field = 499;
 
   void main() {
     this.port.receive((ignoredMessage, reply) {
       reply.send(field, null);
       this.port.close();
     });
   }
 }
 
 void test(TestExpectation expect) {
   ConstructorTest test = new ConstructorTest();
   expect.completes(test.spawn()).then((SendPort port) {
     ReceivePort reply = port.call("ignored");
     reply.receive(expect.runs2((message, replyPort) {
       Expect.equals(499, message);
       expect.succeeded();
     }));
   });
 }
 
 main() {
   runTests([test]);
 }