Move isolate tests to lib/isolate.

tests/lib/async/future_constructor_test.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 future_test;
 
 import "package:expect/expect.dart";
 import 'dart:async';
-import 'dart:isolate';
 
 main() {
   compare(func) {
     // Compare the results of the following two futures.
     Future f1 = new Future(func);
     Future f2 = new Future.value().then((_) => func());
     f2.catchError((_){});  // I'll get the error later.
     f1.then((v1) { f2.then((v2) { Expect.equals(v1, v2); }); },
             onError: (e1) {
               f2.then((_) { Expect.fail("Expected error"); },
                       onError: (e2) {
                          Expect.equals(e1, e2);
                       });
             });
   }
   Future val = new Future.value(42);
   Future err1 = new Future.error("Error")..catchError((_){});
   compare(() => 42);
   compare(() => val);
   compare(() { throw "Flif"; });
   compare(() => err1);
   bool hasExecuted = false;
   compare(() {
     hasExecuted = true;
     return 499;
   });
   Expect.isFalse(hasExecuted);
 }