Update ObjectToString to Harmony-draft algorithm

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 144 matching lines @@
 DEFINE_IMPLICATION(harmony, es_staging)
 
 #define HARMONY_FEATURES(V)                                       \
   V(harmony_scoping, "harmony block scoping")                     \
   V(harmony_modules, "harmony modules (implies block scoping)")   \
   V(harmony_strings, "harmony strings")                           \
   V(harmony_arrays, "harmony arrays")                             \
   V(harmony_classes, "harmony classes")                           \
   V(harmony_object_literals, "harmony object literal extensions") \
   V(harmony_regexps, "reg-exp related harmony features")          \
-  V(harmony_arrow_functions, "harmony arrow functions")
+  V(harmony_arrow_functions, "harmony arrow functions")           \
+  V(harmony_tostring, "harmony Symbol.toStringTag")
 
 #define STAGED_FEATURES(V) \
   V(harmony_numeric_literals, "harmony numeric literals (0o77, 0b11)")
 
 #define SHIPPING_FEATURES(V)
 
 #define FLAG_FEATURES(id, description)           \
   DEFINE_BOOL(id, false, "enable " #description) \
   DEFINE_IMPLICATION(harmony, id)
 
@@ skipping 772 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