Test [[IsHTMLDDA]] object as "prototype" of superclass (#2702)

test/annexB/language/statements/class/subclass/superclass-prototype-emulates-undefined.js

@@ -0,0 +1,29 @@
+// Copyright (C) 2020 Alexey Shvayka. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-runtime-semantics-classdefinitionevaluation
+description: >
+  [[IsHTMLDDA]] object as "prototype" of superclass: `null` check uses strict equality.
+info: |
+  ClassDefinitionEvaluation
+
+  [...]
+  5. Else,
+    [...]
+    g. Else,
+      i. Let protoParent be ? Get(superclass, "prototype").
+      ii. If Type(protoParent) is neither Object nor Null, throw a TypeError exception.
+      iii. Let constructorParent be superclass.
+  6. Let proto be OrdinaryObjectCreate(protoParent).
+  [...]
+features: [class, IsHTMLDDA]
+---*/
+
+function Superclass() {}
+Superclass.prototype = $262.IsHTMLDDA;
+
+class C extends Superclass {}
+var c = new C();
+
+assert(c instanceof C);
+assert(c instanceof Superclass);