[es6] Introduce a dedicated JSIteratorResult type.

src/objects-debug.cc

Index: src/objects-debug.cc
diff --git a/src/objects-debug.cc b/src/objects-debug.cc
index 0dafe03e7a88658e5acb0698d21d15387274a221..094658550507b9a6fd50948e8013e29bb26a7eac 100644
--- a/src/objects-debug.cc
+++ b/src/objects-debug.cc
@@ -143,6 +143,9 @@ void HeapObject::HeapObjectVerify() {
     case JS_MAP_ITERATOR_TYPE:
       JSMapIterator::cast(this)->JSMapIteratorVerify();
       break;
+    case JS_ITERATOR_RESULT_TYPE:
+      JSIteratorResult::cast(this)->JSIteratorResultVerify();
+      break;
     case JS_WEAK_MAP_TYPE:
       JSWeakMap::cast(this)->JSWeakMapVerify();
       break;
@@ -739,6 +742,14 @@ void JSMapIterator::JSMapIteratorVerify() {
 }
 
 
+void JSIteratorResult::JSIteratorResultVerify() {
+  CHECK(IsJSIteratorResult());
+  JSObjectVerify();
+  VerifyPointer(done());
+  VerifyPointer(value());
+}
+
+
 void JSWeakMap::JSWeakMapVerify() {
   CHECK(IsJSWeakMap());
   JSObjectVerify();