Ensure class prototype objects have the right Map::constructor field

test/mjsunit/harmony/regress/regress-3750.js

Index: test/mjsunit/harmony/regress/regress-3750.js
diff --git a/test/message/super-constructor.js b/test/mjsunit/harmony/regress/regress-3750.js
similarity index 75%
copy from test/message/super-constructor.js
copy to test/mjsunit/harmony/regress/regress-3750.js
index 9c96d9bc34ada080b5a90e78fa9b8f967da5ca66..d1f21f9bd39a088f51b25d53ad32ef98d40d0c1e 100644
--- a/test/message/super-constructor.js
+++ b/test/mjsunit/harmony/regress/regress-3750.js
@@ -4,11 +4,5 @@
 //
 // Flags: --harmony-classes
 'use strict';
-
-class C {
-  constructor() {
-    super(this.x);
-  }
-}
-
-new C();
+class Example { }
+Object.observe(Example.prototype, function(){});