[strong] Implement revised strong class semantics

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

Index: test/mjsunit/strong/class-object-frozen.js
diff --git a/test/mjsunit/strong/class-object-frozen.js b/test/mjsunit/strong/class-object-frozen.js
index 49426d8bb29fd20bb74d5adb39457bf129857f8a..2c442c0d5168258986211dd297b7ac05907b459f 100644
--- a/test/mjsunit/strong/class-object-frozen.js
+++ b/test/mjsunit/strong/class-object-frozen.js
@@ -79,3 +79,20 @@ testStrongClass(getClassExprStrong);
   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);
+})();