[api] Prototype WeakRef implementation

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 189 matching lines @@
   V(harmony_sharedarraybuffer, "harmony sharedarraybuffer")             \
   V(harmony_do_expressions, "harmony do-expressions")                   \
   V(harmony_class_fields, "harmony public fields in class literals")    \
   V(harmony_async_iteration, "harmony async iteration")                 \
   V(harmony_dynamic_import, "harmony dynamic import")                   \
   V(harmony_promise_finally, "harmony Promise.prototype.finally")       \
   V(harmony_strict_legacy_accessor_builtins,                            \
     "treat __defineGetter__ and related functions as strict")           \
   V(harmony_restrict_constructor_return,                                \
     "harmony disallow non undefined primitive return value from class " \
-    "constructor")
+    "constructor")                                                      \
+  V(harmony_weakref, "harmony WeakRef")
 
 // Features that are complete (but still behind --harmony/es-staging flag).
 #define HARMONY_STAGED(V)                                                \
   V(harmony_function_tostring, "harmony Function.prototype.toString")    \
   V(harmony_regexp_dotall, "harmony regexp dotall flag")                 \
   V(harmony_regexp_lookbehind, "harmony regexp lookbehind")              \
   V(harmony_regexp_named_captures, "harmony regexp named captures")      \
   V(harmony_regexp_property, "harmony unicode regexp property classes")  \
   V(harmony_object_rest_spread, "harmony object rest spread properties") \
   V(harmony_template_escapes,                                            \
@@ skipping 1130 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