[date] Add ICU backend for timezone info behind a flag

src/flag-definitions.h

Index: src/flag-definitions.h
diff --git a/src/flag-definitions.h b/src/flag-definitions.h
index 2c0e3a1b666d98f2100c19cf9cd6f8a35906e39c..bafa8821677bfb42024ce25fb7b6ae05d3b28bb0 100644
--- a/src/flag-definitions.h
+++ b/src/flag-definitions.h
@@ -194,7 +194,7 @@ DEFINE_IMPLICATION(es_staging, harmony_regexp_lookbehind)
 DEFINE_IMPLICATION(es_staging, move_object_start)
 
 // Features that are still work in progress (behind individual flags).
-#define HARMONY_INPROGRESS(V)                                           \
+#define HARMONY_INPROGRESS_BASE(V)                                      \
   V(harmony_array_prototype_values, "harmony Array.prototype.values")   \
   V(harmony_function_sent, "harmony function.sent")                     \
   V(harmony_tailcalls, "harmony tail calls")                            \
@@ -208,6 +208,14 @@ DEFINE_IMPLICATION(es_staging, move_object_start)
   V(harmony_dynamic_import, "harmony dynamic import")                   \
   V(harmony_promise_finally, "harmony Promise.prototype.finally")
 
+#ifdef V8_I18N_SUPPORT
+#define HARMONY_INPROGRESS(V) \
+  HARMONY_INPROGRESS_BASE(V)  \
+  V(icu_timezone_data, "get information about timezones from ICU")
+#else
+#define HARMONY_INPROGRESS(V) HARMONY_INPROGRESS_BASE(V)
+#endif
+
 // Features that are complete (but still behind --harmony/es-staging flag).
 #define HARMONY_STAGED(V)                                                \
   V(harmony_regexp_lookbehind, "harmony regexp lookbehind")              \