[es6] Initial steps towards a correct implementation of IsCallable.

src/string.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 (function(global, utils) {
 
 %CheckIsBootstrapping();
 
 // -------------------------------------------------------------------
 // Imports
@@ skipping 230 matching lines @@
   // .... special case that replaces with one single character
   // ...... function replace
   // ...... string replace (with $-expansion)
 
   if (IS_REGEXP(search)) {
     // Emulate RegExp.prototype.exec's side effect in step 5, even if
     // value is discarded.
     var lastIndex = search.lastIndex;
     TO_INTEGER_FOR_SIDE_EFFECT(lastIndex);
 
-    if (!IS_SPEC_FUNCTION(replace)) {
+    if (!IS_CALLABLE(replace)) {
       replace = TO_STRING_INLINE(replace);
 
       if (!search.global) {
         // Non-global regexp search, string replace.
         var match = RegExpExec(search, subject, 0);
         if (match == null) {
           search.lastIndex = 0
           return subject;
         }
         if (replace.length == 0) {
@@ skipping 46 matching lines @@
     // replaced by a simple string and only pays off for long strings.
     return %StringReplaceOneCharWithString(subject, search, replace);
   }
   var start = %StringIndexOf(subject, search, 0);
   if (start < 0) return subject;
   var end = start + search.length;
 
   var result = %_SubString(subject, 0, start);
 
   // Compute the string to replace with.
-  if (IS_SPEC_FUNCTION(replace)) {
+  if (IS_CALLABLE(replace)) {
     var receiver = UNDEFINED;
     result += %_CallFunction(receiver, search, start, subject, replace);
   } else {
     reusableMatchInfo[CAPTURE0] = start;
     reusableMatchInfo[CAPTURE1] = end;
     result = ExpandReplacement(TO_STRING_INLINE(replace),
                                subject,
                                reusableMatchInfo,
                                result);
   }
@@ skipping 875 matching lines @@
   to.StringLastIndexOf = StringLastIndexOfJS;
   to.StringMatch = StringMatchJS;
   to.StringReplace = StringReplace;
   to.StringSlice = StringSlice;
   to.StringSplit = StringSplitJS;
   to.StringSubstr = StringSubstr;
   to.StringSubstring = StringSubstring;
 });
 
 })