[es6] Reintroduce the instanceof operator in the backends.

src/flag-definitions.h

 // Copyright 2012 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.
 
 // This file defines all of the flags.  It is separated into different section,
 // for Debug, Release, Logging and Profiling, etc.  To add a new flag, find the
 // correct section, and use one of the DEFINE_ macros, without a trailing ';'.
 //
 // This include does not have a guard, because it is a template-style include,
 // which can be included multiple times in different modes.  It expects to have
@@ skipping 262 matching lines @@
 DEFINE_INT(page_promotion_threshold, 70,
            "min percentage of live bytes on a page to enable fast evacuation")
 DEFINE_BOOL(trace_pretenuring, false,
             "trace pretenuring decisions of HAllocate instructions")
 DEFINE_BOOL(trace_pretenuring_statistics, false,
             "trace allocation site pretenuring statistics")
 DEFINE_BOOL(track_fields, true, "track fields with only smi values")
 DEFINE_BOOL(track_double_fields, true, "track fields with double values")
 DEFINE_BOOL(track_heap_object_fields, true, "track fields with heap values")
 DEFINE_BOOL(track_computed_fields, true, "track computed boilerplate fields")
-DEFINE_BOOL(harmony_instanceof_opt, true, "optimize ES6 instanceof support")
 DEFINE_IMPLICATION(track_double_fields, track_fields)
 DEFINE_IMPLICATION(track_heap_object_fields, track_fields)
 DEFINE_IMPLICATION(track_computed_fields, track_fields)
 DEFINE_BOOL(track_field_types, true, "track field types")
 DEFINE_IMPLICATION(track_field_types, track_fields)
 DEFINE_IMPLICATION(track_field_types, track_heap_object_fields)
 DEFINE_BOOL(smi_binop, true, "support smi representation in binary operations")
 
 // Flags for optimization types.
 DEFINE_BOOL(optimize_for_size, false,
@@ skipping 895 matching lines @@
 #undef DEFINE_ALIAS_FLOAT
 #undef DEFINE_ALIAS_ARGS
 
 #undef FLAG_MODE_DECLARE
 #undef FLAG_MODE_DEFINE
 #undef FLAG_MODE_DEFINE_DEFAULTS
 #undef FLAG_MODE_META
 #undef FLAG_MODE_DEFINE_IMPLICATIONS
 
 #undef COMMA