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

frog/leg/lib/core.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('core');
 
 #import('coreimpl.dart');
 
 #import('js_helper.dart'); // TODO(ahe): remove this import.
 
 #source('../../../corelib/src/bool.dart');
 #source('../../../corelib/src/collection.dart');
 #source('../../../corelib/src/comparable.dart');
 #source('../../../corelib/src/date.dart');
 #source('../../../corelib/src/double.dart');
 #source('../../../corelib/src/duration.dart');
 #source('../../../corelib/src/exceptions.dart');
 #source('../../../corelib/src/expect.dart');
 #source('../../../corelib/src/function.dart');
 #source('../../../corelib/src/future.dart');
 #source('../../../corelib/src/hashable.dart');
 #source('../../../corelib/src/int.dart');
-#source('../../../corelib/src/isolate.dart');
 #source('../../../corelib/src/iterable.dart');
 #source('../../../corelib/src/iterator.dart');
 #source('../../../corelib/src/list.dart');
 #source('../../../corelib/src/map.dart');
 #source('../../../corelib/src/math.dart');
 #source('../../../corelib/src/num.dart');
 #source('../../../corelib/src/options.dart');
 #source('../../../corelib/src/pattern.dart');
 #source('../../../corelib/src/queue.dart');
 #source('../../../corelib/src/regexp.dart');
 #source('../../../corelib/src/set.dart');
 #source('../../../corelib/src/stopwatch.dart');
 #source('../../../corelib/src/string.dart');
 #source('../../../corelib/src/string_buffer.dart');
 #source('../../../corelib/src/strings.dart');
 #source('../../../corelib/src/time_zone.dart');
 #source('mock.dart');
 #source('clock.dart');
 
 void print(var obj) => Primitives.printString(obj.toString());
 
 class Object {
   String toString() => Primitives.objectToString(this);
 
   void noSuchMethod(String name, List args) {
     throw new NoSuchMethodException(this, name, args);
   }
 }