Add tests for Subclassing the built-in Map Objects

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

@@ -0,0 +1,26 @@
+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 23.1.1
+description: Subclassing the Map object
+info: >
+  23.1.1 The Map Constructor
+
+  ...
+
+  The Map 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 Map behaviour must include a super call to the
+  Map constructor to create and initialize the subclass instance with the
+  internal state necessary to support the Map.prototype built-in methods.
+---*/
+
+class M extends Map {}
+
+var map = new M([{ 'foo': 'bar' }]);
+
+assert.sameValue(map.size, 1);
+
+map.set('bar', 'baz');
+
+assert.sameValue(map.size, 2);

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

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+// Copyright (C) 2016 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+es6id: 23.1.1
+description: Super need to be called to initialize internals
+info: >
+  23.1.1 The Map Constructor
+
+  ...
+
+  The Map 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 Map behaviour must include a super call to the
+  Map constructor to create and initialize the subclass instance with the
+  internal state necessary to support the Map.prototype built-in methods.
+---*/
+
+class M1 extends Map {
+  constructor() {}
+}
+
+assert.throws(ReferenceError, function() {
+  new M1();
+});
+
+class M2 extends Map {
+  constructor() {
+    super();
+  }
+}
+
+new M2();