Add ES2015 RegExp full subclassing semantics behind a flag

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index db4a157623df5214b7ea5028cbef0981a7bc517d..05bd5e819bd00eeedd4c11bd959a1c36aa57f7e4 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -2363,6 +2363,7 @@ EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_regexps)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_unicode_regexps)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_do_expressions)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_iterator_close)
+EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_regexp_exec)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_regexp_lookbehind)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_regexp_property)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_function_name)
@@ -2941,6 +2942,8 @@ bool Genesis::InstallExperimentalNatives() {
   static const char* harmony_simd_natives[] = {"native harmony-simd.js",
                                                nullptr};
   static const char* harmony_do_expressions_natives[] = {nullptr};
+  static const char* harmony_regexp_exec_natives[] = {
+      "native harmony-regexp-exec.js", nullptr};
   static const char* harmony_regexp_subclass_natives[] = {nullptr};
   static const char* harmony_regexp_lookbehind_natives[] = {nullptr};
   static const char* harmony_instanceof_natives[] = {nullptr};