Update ObjectToString to Harmony-draft algorithm

src/collection.js

Index: src/collection.js
diff --git a/src/collection.js b/src/collection.js
index 0027bd732041f94ccf81dbfe3256c4f75d680c5a..ff747accff85ed33cb62ad40c42aa805c1abd4af 100644
--- a/src/collection.js
+++ b/src/collection.js
@@ -126,6 +126,8 @@ function SetUpSet() {
   %SetCode($Set, SetConstructor);
   %FunctionSetPrototype($Set, new $Object());
   %AddNamedProperty($Set.prototype, "constructor", $Set, DONT_ENUM);
+  %AddNamedProperty(
+      $Set.prototype, symbolToStringTag, "Set", DONT_ENUM | READ_ONLY);
 
   %FunctionSetLength(SetForEach, 1);
 
@@ -268,6 +270,8 @@ function SetUpMap() {
   %SetCode($Map, MapConstructor);
   %FunctionSetPrototype($Map, new $Object());
   %AddNamedProperty($Map.prototype, "constructor", $Map, DONT_ENUM);
+  %AddNamedProperty(
+      $Map.prototype, symbolToStringTag, "Map", DONT_ENUM | READ_ONLY);
 
   %FunctionSetLength(MapForEach, 1);