Add a --harmony-object-observe runtime flag (on by default)

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 192 matching lines @@
 #define HARMONY_STAGED(V)                                    \
   V(harmony_tostring, "harmony toString")                    \
   V(harmony_concat_spreadable, "harmony isConcatSpreadable") \
   V(harmony_rest_parameters, "harmony rest parameters")
 
 // Features that are shipping (turned on by default, but internal flag remains).
 #define HARMONY_SHIPPING(V)                                             \
   V(harmony_arrow_functions, "harmony arrow functions")                 \
   V(harmony_computed_property_names, "harmony computed property names") \
   V(harmony_new_target, "harmony new.target")                           \
+  V(harmony_object_observe, "harmony Object.observe")                   \
   V(harmony_spreadcalls, "harmony spread-calls")                        \
   V(harmony_spread_arrays, "harmony spread in array literals")          \
   V(harmony_unicode, "harmony unicode escapes")                         \
   V(harmony_object, "harmony Object methods")
 
 // Once a shipping feature has proved stable in the wild, it will be dropped
 // from HARMONY_SHIPPING, all occurrences of the FLAG_ variable are removed,
 // and associated tests are moved from the harmony directory to the appropriate
 // esN directory.
 
@@ skipping 853 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