[builtins] Also migrate String.prototype.toLowerCase/toUpperCase to C++.

src/js/string.js

Index: src/js/string.js
diff --git a/src/js/string.js b/src/js/string.js
index 33a3e72143ca5020c8a9441d6a9b08f63c581f04..cd1bcdbc29216d5526974ef4b4e78b96b5aa34b8 100644
--- a/src/js/string.js
+++ b/src/js/string.js
@@ -487,38 +487,6 @@ function StringSubstr(start, n) {
 }
 
 
-// ECMA-262, 15.5.4.16
-function StringToLowerCaseJS() {
-  CHECK_OBJECT_COERCIBLE(this, "String.prototype.toLowerCase");
-
-  return %StringToLowerCase(TO_STRING(this));
-}
-
-
-// ECMA-262, 15.5.4.17
-function StringToLocaleLowerCase() {
-  CHECK_OBJECT_COERCIBLE(this, "String.prototype.toLocaleLowerCase");
-
-  return %StringToLowerCase(TO_STRING(this));
-}
-
-
-// ECMA-262, 15.5.4.18
-function StringToUpperCaseJS() {
-  CHECK_OBJECT_COERCIBLE(this, "String.prototype.toUpperCase");
-
-  return %StringToUpperCase(TO_STRING(this));
-}
-
-
-// ECMA-262, 15.5.4.19
-function StringToLocaleUpperCase() {
-  CHECK_OBJECT_COERCIBLE(this, "String.prototype.toLocaleUpperCase");
-
-  return %StringToUpperCase(TO_STRING(this));
-}
-
-
 // ES6 draft, revision 26 (2014-07-18), section B.2.3.2.1
 function HtmlEscape(str) {
   return %_Call(StringReplace, TO_STRING(str), /"/g, """);
@@ -827,10 +795,6 @@ utils.InstallFunctions(GlobalString.prototype, DONT_ENUM, [
   "substring", StringSubstring,
   "substr", StringSubstr,
   "startsWith", StringStartsWith,
-  "toLowerCase", StringToLowerCaseJS,
-  "toLocaleLowerCase", StringToLocaleLowerCase,
-  "toUpperCase", StringToUpperCaseJS,
-  "toLocaleUpperCase", StringToLocaleUpperCase,
 
   "link", StringLink,
   "anchor", StringAnchor,