Merge kernel closure conversion into the Dart SDK

pkg/kernel/testcases/closures/for_in_closure.dart

+// Copyright (c) 2016, 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.md file.
+
+const numbers = const <int>[0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
+
+main() {
+  var closures = [];
+  for (int i in numbers) {
+    closures.add(() => i);
+  }
+  int sum = 0;
+  for (Function f in closures) {
+    sum += f();
+  }
+  // This formula is credited to Gauss. Search for "Gauss adding 1 to 100".
+  int expectedSum = (numbers.length - 1) * numbers.length ~/ 2;
+  if (expectedSum != sum) {
+    throw new Exception("Unexpected sum = $sum != $expectedSum");
+  }
+}