Revert of [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 cd1bcdbc29216d5526974ef4b4e78b96b5aa34b8..33a3e72143ca5020c8a9441d6a9b08f63c581f04 100644
--- a/src/js/string.js
+++ b/src/js/string.js
@@ -487,6 +487,38 @@
 }
 
 
+// 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, """);
@@ -795,6 +827,10 @@
   "substring", StringSubstring,
   "substr", StringSubstr,
   "startsWith", StringStartsWith,
+  "toLowerCase", StringToLowerCaseJS,
+  "toLocaleLowerCase", StringToLocaleLowerCase,
+  "toUpperCase", StringToUpperCaseJS,
+  "toLocaleUpperCase", StringToLocaleUpperCase,
 
   "link", StringLink,
   "anchor", StringAnchor,