ES6: Make Map/Set constructors support iterable values

src/weak_collection.js

Index: src/weak_collection.js
diff --git a/src/weak_collection.js b/src/weak_collection.js
index 73dd9de6ba9aa5c48d16596ffde2c015e1764673..1160176d66f6c34b8cf8acb59d0841d832055aae 100644
--- a/src/weak_collection.js
+++ b/src/weak_collection.js
@@ -23,7 +23,7 @@ function WeakMapConstructor(iterable) {
   var iter, adder;
 
   if (!IS_NULL_OR_UNDEFINED(iterable)) {
-    iter = GetIterator(iterable);
+    iter = GetIterator(ToObject(iterable));
     adder = this.set;
     if (!IS_SPEC_FUNCTION(adder)) {
       throw MakeTypeError('property_not_function', ['set', this]);
@@ -139,7 +139,7 @@ function WeakSetConstructor(iterable) {
   var iter, adder;
 
   if (!IS_NULL_OR_UNDEFINED(iterable)) {
-    iter = GetIterator(iterable);
+    iter = GetIterator(ToObject(iterable));
     adder = this.add;
     if (!IS_SPEC_FUNCTION(adder)) {
       throw MakeTypeError('property_not_function', ['add', this]);