Update ObjectToString to Harmony-draft algorithm

src/v8natives.js

Index: src/v8natives.js
diff --git a/src/v8natives.js b/src/v8natives.js
index 1d2e03000763062f3777e1a565e1792227f3e634..7a1f25bdd9292641a96f4a614d1ff5fb5e2b5aa2 100644
--- a/src/v8natives.js
+++ b/src/v8natives.js
@@ -214,12 +214,34 @@ SetUpGlobal();
 
 // ----------------------------------------------------------------------------
 // Object
+var kBuiltinStringTags = {

[caitp (gmail), 2014/10/10 14:56:28]

ObjectCreate(null) would be better, I guess

[rossberg, 2014/10/17 11:19:30]

Yes, the prototype has to be null, otherwise the code below is wrong. You could
do "__proto__: null".

+  "Arguments": "[object ~Arguments]",
+  "Array": "[object ~Array]",
+  "Boolean": "[object ~Boolean]",
+  "Date": "[object ~Date]",
+  "Error": "[object ~Error]",
+  "Function": "[object ~Function]",
+  "Number": "[object ~Number]",
+  "RegExp": "[object ~RegExp]",
+  "String": "[object ~String]"
+};
 
 // ECMA-262 - 15.2.4.2
+// ES6 draft 08-24-14, section 19.1.3.6
 function ObjectToString() {
   if (IS_UNDEFINED(this) && !IS_UNDETECTABLE(this)) return "[object Undefined]";
   if (IS_NULL(this)) return "[object Null]";
-  return "[object " + %_ClassOf(ToObject(this)) + "]";
+  var O = ToObject(this);
+  var builtinTag = %_ClassOf(O);
+  var tag = O[symbolToStringTag];

[rossberg, 2014/10/17 11:19:30]

We need some way of putting this new behaviour behind a flag first
(--harmony-tostring). You probably need to introduce a runtime function to query
the flag here.

+  if (IS_UNDEFINED(tag)) tag = builtinTag;

[rossberg, 2014/10/17 11:19:30]

Style nit: new line if there is an 'else'.

+  else {
+    if (!IS_STRING(tag)) return "[object ???]";

[rossberg, 2014/10/17 11:19:30]

Same here. Can also merge into an 'else if' with the above 'else'.

+    else if (tag !== builtinTag && IS_STRING(kBuiltinStringTags[tag])) {
+      return kBuiltinStringTags[tag];

[arv (Not doing code reviews), 2014/10/17 14:40:51]

Maybe make the kBuiltinStringTags a "set" and then concat the string on demand.
The usage of these seems very low so having the extra strings in memory does not
seem worth it.

var kBuiltinStringTags = {
  __proto__: null,
  "Arguments": true,
  "Array": true,
  "Boolean": true,
  "Date": true,
  "Error": true,
  "Function": true,
  "Number": true,
  "RegExp": true,
  "String": true,
};

...


} else if (tag !== builtinTag && kBuiltinStringTags[tag]) {
  return "[object ~" + tag + "]";
}

+    }
+  }
+  return "[object " + tag + "]";
 }