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 37639ece53fa34dc45c532641ac23ab48c529984..b87b26422c20e05e1da734eb451dc376fa681108 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -3004,6 +3004,8 @@ 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++) {
@@ -3023,6 +3025,7 @@ 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
   }