Implement Dart 1.0 LUB algorithm (for interface types) in kernel.

pkg/kernel/test/heap_test.dart

+// Copyright (c) 2017, 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.
+
+import 'package:kernel/heap.dart';
+import 'package:test/test.dart';
+
+main() {
+  test('sort', () {
+    var values = <int>[3, 1, 4, 1, 5, 9, 2, 6];

[ahe, 2017/05/01 16:50:34]

Would it make sense to test a list that is sorted, and one that is reversed
sorted?

[Paul Berry, 2017/05/01 18:12:14]

Yes, good idea.  Done.

+    var heap = new _intHeap();
+    values.forEach(heap.add);
+    values.sort();
+    var result = <int>[];
+    while (heap.isNotEmpty) {
+      expect(heap.isEmpty, isFalse);
+      result.add(heap.remove());
+    }
+    expect(heap.isEmpty, isTrue);
+    expect(result, values);
+  });
+}
+
+class _intHeap extends Heap<int> {
+  bool sortsBefore(int a, int b) => a < b;
+}