Avoid calling the builtin String.prototype.split in Intl

src/js/i18n.js

Index: src/js/i18n.js
diff --git a/src/js/i18n.js b/src/js/i18n.js
index dd85a0526495c926bc55ba011769dca720059d3c..e018262ca2b76fedce02c82fc6d8ce9866e8b747 100644
--- a/src/js/i18n.js
+++ b/src/js/i18n.js
@@ -41,7 +41,6 @@ var resolvedSymbol = utils.ImportNow("intl_resolved_symbol");
 var SetFunctionName = utils.SetFunctionName;
 var StringIndexOf;
 var StringLastIndexOf;
-var StringSplit;
 var StringSubstr;
 var StringSubstring;
 
@@ -57,7 +56,6 @@ utils.Import(function(from) {
   InternalRegExpReplace = from.InternalRegExpReplace;
   StringIndexOf = from.StringIndexOf;
   StringLastIndexOf = from.StringLastIndexOf;
-  StringSplit = from.StringSplit;
   StringSubstr = from.StringSubstr;
   StringSubstring = from.StringSubstring;
 });
@@ -125,6 +123,15 @@ function AddBoundMethod(obj, methodName, implementation, length, type) {
   %SetNativeFlag(getter);
 }
 
+// Special StringSplit function for this file; does not work with RegExps
+// or access Symbol.split, but per spec, is just for strings.
+function StringSplit(separator, limit) {
+  var subject = TO_STRING(this);
+  var separator_string = TO_STRING(separator);
+  limit = (IS_UNDEFINED(limit)) ? kMaxUint32 : TO_UINT32(limit);

[Yang, 2016/07/07 09:13:01]

I don't think StringSplit is used with the optional limit argument at all in
this file.
Also, can we figure out whether TO_STRING is necessary at all? If not, we could
simply call %StringSplit at all call sites, or some form of
%StringSplit(TO_STRING(a), TO_STRING(b), kMaxUint32), instead of using %_Call.

[Dan Ehrenberg, 2016/07/07 18:35:42]

That's true; I don't see a real need to call TO_STRING at all, except as
defensive programming. I initially prototyped it with just calling %StringSplit
all over the place, but I was thinking we might want to limit the number of
callsites to a runtime function and reduce the number of variables changed in
this patch. The new version just calls %StringSplit.

+  return %StringSplit(this, separator, limit);
+}
+
 // -------------------------------------------------------------------
 
 var Intl = {};