[es6] Reintroduce the instanceof operator in the backends.

src/lookup.h

 // Copyright 2014 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_LOOKUP_H_
 #define V8_LOOKUP_H_
 
 #include "src/factory.h"
 #include "src/isolate.h"
 #include "src/objects.h"
@@ skipping 245 matching lines @@
         IsElement() ? GetInterceptor<true>(JSObject::cast(*holder_))
                     : GetInterceptor<false>(JSObject::cast(*holder_));
     return handle(result, isolate_);
   }
   Handle<Object> GetDataValue() const;
   void WriteDataValue(Handle<Object> value);
   inline void UpdateProtector() {
     if (IsElement()) return;
     if (*name_ == heap()->is_concat_spreadable_symbol() ||
         (FLAG_harmony_species && (*name_ == heap()->constructor_string() ||
-                                  *name_ == heap()->species_symbol()))) {
+                                  *name_ == heap()->species_symbol())) ||
+        (FLAG_harmony_instanceof &&
+         (*name_ == heap()->has_instance_symbol()))) {
       InternalUpdateProtector();
     }
   }
 
  private:
   void InternalUpdateProtector();
 
   enum class InterceptorState {
     kUninitialized,
     kSkipNonMasking,
@@ skipping 83 matching lines @@
   const Handle<JSReceiver> initial_holder_;
   const uint32_t index_;
   uint32_t number_;
 };
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_LOOKUP_H_