[es6] Reintroduce the instanceof operator in the backends.

src/isolate-inl.h

 // 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.
 
 #ifndef V8_ISOLATE_INL_H_
 #define V8_ISOLATE_INL_H_
 
 #include "src/isolate.h"
 #include "src/objects-inl.h"
 
@@ skipping 102 matching lines @@
   // All that could be checked reliably is that
   // Array.prototype.constructor == Array. Given that limitation, no check is
   // done here. In place, there are mjsunit tests harmony/array-species* which
   // ensure that behavior is correct in various invalid protector cases.
 
   Cell* species_cell = heap()->species_protector();
   return species_cell->value()->IsSmi() &&
          Smi::cast(species_cell->value())->value() == kArrayProtectorValid;
 }
 
+bool Isolate::IsHasInstanceLookupChainIntact() {
+  if (!FLAG_harmony_instanceof) return true;
+  PropertyCell* has_instance_cell = heap()->has_instance_protector();
+  return has_instance_cell->value() == Smi::FromInt(kArrayProtectorValid);
+}
+
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ISOLATE_INL_H_