[es6] Introduce a dedicated JSIteratorResult type.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index fb574619608153f221f7cdccbb80ffd4199a94b0..1fb035e5eccf338eb9c9ca3c9061c39d967f3951 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -698,6 +698,7 @@ TYPE_CHECKER(JSSet, JS_SET_TYPE)
 TYPE_CHECKER(JSMap, JS_MAP_TYPE)
 TYPE_CHECKER(JSSetIterator, JS_SET_ITERATOR_TYPE)
 TYPE_CHECKER(JSMapIterator, JS_MAP_ITERATOR_TYPE)
+TYPE_CHECKER(JSIteratorResult, JS_ITERATOR_RESULT_TYPE)
 TYPE_CHECKER(JSWeakMap, JS_WEAK_MAP_TYPE)
 TYPE_CHECKER(JSWeakSet, JS_WEAK_SET_TYPE)
 TYPE_CHECKER(JSContextExtensionObject, JS_CONTEXT_EXTENSION_OBJECT_TYPE)
@@ -2144,6 +2145,8 @@ int JSObject::GetHeaderSize() {
       return JSSetIterator::kSize;
     case JS_MAP_ITERATOR_TYPE:
       return JSMapIterator::kSize;
+    case JS_ITERATOR_RESULT_TYPE:
+      return JSIteratorResult::kSize;
     case JS_WEAK_MAP_TYPE:
       return JSWeakMap::kSize;
     case JS_WEAK_SET_TYPE:
@@ -3319,6 +3322,7 @@ CAST_ACCESSOR(JSReceiver)
 CAST_ACCESSOR(JSRegExp)
 CAST_ACCESSOR(JSSet)
 CAST_ACCESSOR(JSSetIterator)
+CAST_ACCESSOR(JSIteratorResult)
 CAST_ACCESSOR(JSTypedArray)
 CAST_ACCESSOR(JSValue)
 CAST_ACCESSOR(JSWeakMap)
@@ -7795,6 +7799,10 @@ Object* JSMapIterator::CurrentValue() {
 }
 
 
+ACCESSORS(JSIteratorResult, done, Object, kDoneOffset)
+ACCESSORS(JSIteratorResult, value, Object, kValueOffset)
+
+
 String::SubStringRange::SubStringRange(String* string, int first, int length)
     : string_(string),
       first_(first),