[es6] Introduce a dedicated JSIteratorResult type.

src/objects-printer.cc

Index: src/objects-printer.cc
diff --git a/src/objects-printer.cc b/src/objects-printer.cc
index 73fa5b12e4ef7732a05c04502726267a4d1c3f34..5be28760b47c1d50f879eb42fdb4029fd9a68758 100644
--- a/src/objects-printer.cc
+++ b/src/objects-printer.cc
@@ -144,6 +144,9 @@ void HeapObject::HeapObjectPrint(std::ostream& os) {  // NOLINT
     case JS_MAP_ITERATOR_TYPE:
       JSMapIterator::cast(this)->JSMapIteratorPrint(os);
       break;
+    case JS_ITERATOR_RESULT_TYPE:
+      JSIteratorResult::cast(this)->JSIteratorResultPrint(os);
+      break;
     case JS_WEAK_MAP_TYPE:
       JSWeakMap::cast(this)->JSWeakMapPrint(os);
       break;
@@ -756,6 +759,15 @@ void JSMapIterator::JSMapIteratorPrint(std::ostream& os) {  // NOLINT
 }
 
 
+void JSIteratorResult::JSIteratorResultPrint(std::ostream& os) {  // NOLINT
+  HeapObject::PrintHeader(os, "JSIteratorResult");
+  os << " - map = " << reinterpret_cast<void*>(map()) << "\n";
+  os << " - done = " << Brief(done()) << "\n";
+  os << " - value = " << Brief(value()) << "\n";
+  os << "\n";
+}
+
+
 void JSWeakMap::JSWeakMapPrint(std::ostream& os) {  // NOLINT
   HeapObject::PrintHeader(os, "JSWeakMap");
   os << " - map = " << reinterpret_cast<void*>(map()) << "\n";