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

test/webkit/webkit.status

Index: test/webkit/webkit.status
diff --git a/test/webkit/webkit.status b/test/webkit/webkit.status
index ed523783183ffe6f53d3c8bbe0f9a0aa77b46565..0ab809ff426c7d3efa588a900da5a2604cfc724d 100644
--- a/test/webkit/webkit.status
+++ b/test/webkit/webkit.status
@@ -37,6 +37,9 @@
   'fast/js/deep-recursion-test': [PASS, NO_VARIANTS],
   # Irregexp interpreter overflows stack. We should just not crash.
   'fast/js/regexp-stack-overflow': [PASS, FAIL],
+
+  # BUG(v8:4476): fixed but still behind a flag, icu_case_mapping
+  'fast/js/string-capitalization': [FAIL],
 }],  # ALWAYS
 ['mode == debug', {
   # Too slow in debug mode.