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

src/collection.js

Index: src/collection.js
diff --git a/src/collection.js b/src/collection.js
index 718ca9be67e3d3d4e12277429a1e3c7eda3efaf0..315270c352e308244c334aa115aee01bc4ca967d 100644
--- a/src/collection.js
+++ b/src/collection.js
@@ -133,7 +133,7 @@ function SetConstructor(iterable) {
 
   if (!IS_NULL_OR_UNDEFINED(iterable)) {
     var adder = this.add;
-    if (!IS_SPEC_FUNCTION(adder)) {
+    if (!IS_CALLABLE(adder)) {
       throw MakeTypeError(kPropertyNotFunction, 'add', this);
     }
 
@@ -244,7 +244,7 @@ function SetForEach(f, receiver) {
                         'Set.prototype.forEach', this);
   }
 
-  if (!IS_SPEC_FUNCTION(f)) throw MakeTypeError(kCalledNonCallable, f);
+  if (!IS_CALLABLE(f)) throw MakeTypeError(kCalledNonCallable, f);
   var needs_wrapper = false;
   if (IS_NULL(receiver)) {
     if (%IsSloppyModeFunction(f)) receiver = UNDEFINED;
@@ -298,7 +298,7 @@ function MapConstructor(iterable) {
 
   if (!IS_NULL_OR_UNDEFINED(iterable)) {
     var adder = this.set;
-    if (!IS_SPEC_FUNCTION(adder)) {
+    if (!IS_CALLABLE(adder)) {
       throw MakeTypeError(kPropertyNotFunction, 'set', this);
     }
 
@@ -435,7 +435,7 @@ function MapForEach(f, receiver) {
                         'Map.prototype.forEach', this);
   }
 
-  if (!IS_SPEC_FUNCTION(f)) throw MakeTypeError(kCalledNonCallable, f);
+  if (!IS_CALLABLE(f)) throw MakeTypeError(kCalledNonCallable, f);
   var needs_wrapper = false;
   if (IS_NULL(receiver)) {
     if (%IsSloppyModeFunction(f)) receiver = UNDEFINED;