[strong] Implement revised strong class semantics

test/mjsunit/strong/class-object-frozen.js

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Flags: --strong-mode
 
 "use strict";
 
 function getClass() {
   class Foo {
@@ skipping 61 matching lines @@
       static get bar() { return 0 }
       get bar() { return 0 }
     }
     return Foo;
   }
 
   testStrongClass(classFunc);
   assertDoesNotThrow(function(){addProperty(parent)});
   assertDoesNotThrow(function(){convertPropertyToData(parent)});
 })();
+
+// Check strong classes don't freeze their children.
+(function() {
+  let parent = getClassStrong();
+
+  let classFunc = function() {
+    class Foo extends parent {
+      static get bar() { return 0 }
+      get bar() { return 0 }
+    }
+    return Foo;
+  }
+
+  assertThrows(function(){addProperty(parent)}, TypeError);
+  assertThrows(function(){convertPropertyToData(parent)}, TypeError);
+  testWeakClass(classFunc);
+})();