[builtins] Move StringLastIndexOf to a builtin.

src/js/i18n.js

Index: src/js/i18n.js
diff --git a/src/js/i18n.js b/src/js/i18n.js
index 7ccefef928e6990f44396a849d0137938728eda8..16abb8002ce9b67c1e4dfce9fee5f3bcbf5dd0ff 100644
--- a/src/js/i18n.js
+++ b/src/js/i18n.js
@@ -35,7 +35,6 @@ var patternSymbol = utils.ImportNow("intl_pattern_symbol");
 var resolvedSymbol = utils.ImportNow("intl_resolved_symbol");
 var SetFunctionName = utils.SetFunctionName;
 var StringIndexOf;
-var StringLastIndexOf;
 var StringSubstr;
 var StringSubstring;
 
@@ -45,7 +44,6 @@ utils.Import(function(from) {
   InternalRegExpMatch = from.InternalRegExpMatch;
   InternalRegExpReplace = from.InternalRegExpReplace;
   StringIndexOf = from.StringIndexOf;
-  StringLastIndexOf = from.StringLastIndexOf;
   StringSubstr = from.StringSubstr;
   StringSubstring = from.StringSubstring;
 });
@@ -316,7 +314,7 @@ function lookupSupportedLocalesOf(requestedLocales, availableLocales) {
         break;
       }
       // Truncate locale if possible, if not break.
-      var pos = %_Call(StringLastIndexOf, locale, '-');
+      var pos = locale.lastIndexOf('-');

[Benedikt Meurer, 2016/09/14 17:02:32]

This is not correct, because this does a lookup of lastIndexOf on locale each
time you executed it. But String.prototype.lastIndexOf is monkey patchable,
which means you might get a different function here. So you really need to
remember the correct function during bootstrapping. Or even better, put it onto
the native context and call it via %StringLastIndexOf(locale, '-') here, as we
do with other initial functions like %ObjectFreeze, etc.

[petermarshall, 2016/09/15 12:19:59]

Added the runtime function back in as we discussed

       if (pos === -1) {
         break;
       }
@@ -439,7 +437,7 @@ function lookupMatcher(service, requestedLocales) {
         return {'locale': locale, 'extension': extension, 'position': i};
       }
       // Truncate locale if possible.
-      var pos = %_Call(StringLastIndexOf, locale, '-');
+      var pos = locale.lastIndexOf('-');

[Benedikt Meurer, 2016/09/14 17:02:32]

Same here.

       if (pos === -1) {
         break;
       }