Add tests for Subclassing the built-in Set Objects

test/language/subclassing/Set/regular-subclassing.js

+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 23.2.1
+description: Subclassing the Set object
+info: >
+  23.2.1 The Set Constructor
+
+  ...
+
+  The Set constructor is designed to be subclassable. It may be used as the
+  value in an extends clause of a class definition. Subclass constructors that
+  intend to inherit the specified Set behaviour must include a super call to the
+  Set constructor to create and initialize the subclass instance with the
+  internal state necessary to support the Set.prototype built-in methods.
+---*/
+
+class S extends Set {}
+
+var set = new S([{}, {}]);
+
+assert.sameValue(set.size, 2);
+
+set.add({});
+
+assert.sameValue(set.size, 3);

test/language/subclassing/Set/super-must-be-called.js

+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 23.2.1
+description: Super need to be called to initialize internals
+info: >
+  23.2.1 The Set Constructor
+
+  ...
+
+  The Set constructor is designed to be subclassable. It may be used as the
+  value in an extends clause of a class definition. Subclass constructors that
+  intend to inherit the specified Set behaviour must include a super call to the
+  Set constructor to create and initialize the subclass instance with the
+  internal state necessary to support the Set.prototype built-in methods.
+---*/
+
+class S1 extends Set {
+  constructor() {}
+}
+
+assert.throws(ReferenceError, function() {
+  new S1();
+});
+
+class S2 extends Set {
+  constructor() {
+    super();
+  }
+}
+
+new S2();