Migrating a block of dart 1 tests to dart 2

tests/language_strong/closure_cycles_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.
-// Based on dartbug.com/7681
-// Verify that context chains do not lead to unintended memory being held.
-
-library closure_cycles_test;
-
-import "dart:async";
-
-class X {
-  Function onX;
-  X() {
-    Timer.run(() => onX(new Y()));
-  }
-}
-
-class Y {
-  Function onY;
-  var heavyMemory;
-  static var count = 0;
-  Y() {
-    // Consume large amounts of memory per iteration to fail/succeed quicker.
-    heavyMemory = new List(10 * 1024 * 1024);
-    // Terminate the test if we allocated enough memory without running out.
-    if (count++ > 100) return;
-    Timer.run(() => onY());
-  }
-}
-
-void doIt() {
-  var x = new X();
-  x.onX = (y) {
-    y.onY = () {
-      y; // Capturing y can lead to endless context chains!
-      doIt();
-    };
-  };
-}
-
-void main() {
-  doIt();
-}