Correctify instanceof and make it optimizable.

test/mjsunit/regress/regress-4376-3.js

Index: test/mjsunit/regress/regress-4376-3.js
diff --git a/test/message/arrow-formal-parameters.js b/test/mjsunit/regress/regress-4376-3.js
similarity index 52%
copy from test/message/arrow-formal-parameters.js
copy to test/mjsunit/regress/regress-4376-3.js
index edc0c58053524299a9616c57a5a7be2e986cf8f3..3240cf0cd90267d2bfcc3269409a6d64a3d640e8 100644
--- a/test/message/arrow-formal-parameters.js
+++ b/test/mjsunit/regress/regress-4376-3.js
@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --harmony-arrow-functions
-
-(b, a, a, d) => a
+function Foo() {}
+var x = new Foo();
+function foo() { return x instanceof Foo; }
+assertTrue(foo());
+Foo.prototype = 1;
+assertThrows(foo, TypeError);