Use ICU case conversion/transliterator for case conversion behind a flag

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index 9af851f710d25c5476ab924bbbe8850adb9986cb..6dcaff2ccbb7dbe484be6a68482d8a21bd1a4053 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -3018,6 +3018,8 @@ bool Genesis::InstallExperimentalNatives() {
   static const char* harmony_exponentiation_operator_natives[] = {nullptr};
   static const char* harmony_string_padding_natives[] = {
       "native harmony-string-padding.js", nullptr};
+  static const char* icu_case_mapping_natives[] = {"native icu-case-mapping.js",
+                                                   nullptr};
 
   for (int i = ExperimentalNatives::GetDebuggerCount();
        i < ExperimentalNatives::GetBuiltinsCount(); i++) {
@@ -3037,6 +3039,7 @@ bool Genesis::InstallExperimentalNatives() {
     HARMONY_STAGED(INSTALL_EXPERIMENTAL_NATIVES);
     HARMONY_SHIPPING(INSTALL_EXPERIMENTAL_NATIVES);
     INSTALL_EXPERIMENTAL_NATIVES(promise_extra, "");
+    INSTALL_EXPERIMENTAL_NATIVES(icu_case_mapping, "");
 #undef INSTALL_EXPERIMENTAL_NATIVES
   }