Revert of [builtins] Migrate String.prototype.charCodeAt and String.prototype.charAt to TurboFan.

src/js/string.js

Index: src/js/string.js
diff --git a/src/js/string.js b/src/js/string.js
index f0b970a0490d830a9b4b9e5a23bc16ed00d0aefc..ede5f881604b4ab2abaacba6c7a0a29be5db383e 100644
--- a/src/js/string.js
+++ b/src/js/string.js
@@ -54,6 +54,30 @@
     throw MakeTypeError(kNotGeneric, 'String.prototype.valueOf');
   }
   return %_ValueOf(this);
+}
+
+
+// ECMA-262, section 15.5.4.4
+function StringCharAtJS(pos) {
+  CHECK_OBJECT_COERCIBLE(this, "String.prototype.charAt");
+
+  var result = %_StringCharAt(this, pos);
+  if (%_IsSmi(result)) {
+    result = %_StringCharAt(TO_STRING(this), TO_INTEGER(pos));
+  }
+  return result;
+}
+
+
+// ECMA-262 section 15.5.4.5
+function StringCharCodeAtJS(pos) {
+  CHECK_OBJECT_COERCIBLE(this, "String.prototype.charCodeAt");
+
+  var result = %_StringCharCodeAt(this, pos);
+  if (!%_IsSmi(result)) {
+    result = %_StringCharCodeAt(TO_STRING(this), TO_INTEGER(pos));
+  }
+  return result;
 }
 
 
@@ -833,6 +857,13 @@
 
 // -------------------------------------------------------------------
 
+// Set the String function and constructor.
+%FunctionSetPrototype(GlobalString, new GlobalString());
+
+// Set up the constructor property on the String prototype object.
+%AddNamedProperty(
+    GlobalString.prototype, "constructor", GlobalString, DONT_ENUM);
+
 // Set up the non-enumerable functions on the String object.
 utils.InstallFunctions(GlobalString, DONT_ENUM, [
   "fromCharCode", StringFromCharCode,
@@ -844,6 +875,8 @@
 utils.InstallFunctions(GlobalString.prototype, DONT_ENUM, [
   "valueOf", StringValueOf,
   "toString", StringToString,
+  "charAt", StringCharAtJS,
+  "charCodeAt", StringCharCodeAtJS,
   "codePointAt", StringCodePointAt,
   "concat", StringConcat,
   "endsWith", StringEndsWith,
@@ -889,6 +922,7 @@
 
 utils.Export(function(to) {
   to.ExpandReplacement = ExpandReplacement;
+  to.StringCharAt = StringCharAtJS;
   to.StringIndexOf = StringIndexOf;
   to.StringLastIndexOf = StringLastIndexOf;
   to.StringMatch = StringMatchJS;