Remove old isolate API and update all code in the repository to use

tests/isolate/mixed_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.
-
-// Dart test program for testing that heavy and light isolates can be mixed.
-
-#library('MixedTest');
-#import("dart:isolate");
-#import('../../lib/unittest/unittest.dart');
-
-class IsolateA extends Isolate {
-  IsolateA() : super.heavy();
-
-  void main() {
-    this.port.receive((msg, replyTo) {
-      Expect.equals("launch nested!", msg);
-      new IsolateB().spawn().then((SendPort p) {
-        p.call("alive?").then((msg) {
-          Expect.equals("and kicking", msg);
-          replyTo.send(499, null);
-          this.port.close();
-        });
-      });
-    });
-  }
-}
-
-class IsolateB extends Isolate {
-  IsolateB() : super.light();
-
-  void main() {
-    this.port.receive((msg, replyTo) {
-      Expect.equals("alive?", msg);
-      replyTo.send("and kicking", null);
-      this.port.close();
-    });
-  }
-}
-
-main() {
-  test("light isolate can spawn heavy isolate", () {
-    new IsolateA().spawn().then(expectAsync1((SendPort port) {
-      port.call("launch nested!").then(expectAsync1((msg) {
-        Expect.equals(499, msg);
-      }));
-    }));
-  });
-}