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

runtime/vm/snapshot_test.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.
 
+#import("dart:isolate");
+
 class Fields  {
   Fields(int i, int j) : fld1 = i, fld2 = j, fld5 = true {}
   int fld1;
   final int fld2;
   static int fld3;
   static final int fld4 = 10;
   bool fld5;
 }
 class FieldsTest {
   static Fields testMain() {
@@ skipping 1921 matching lines @@
       });
     });
   }
 
   void main() {
     this.port.receive((ignored, replyTo) {
       replyTo.send("foo", null);
     });
   }
 }