[modules] Implement @@iterator on namespace objects.

src/objects-debug.cc

Index: src/objects-debug.cc
diff --git a/src/objects-debug.cc b/src/objects-debug.cc
index afde76404e1dc071547081a79840a66782577420..ec1a1d5d211dc114375e93085ccf40faf05a6a53 100644
--- a/src/objects-debug.cc
+++ b/src/objects-debug.cc
@@ -143,6 +143,9 @@ void HeapObject::HeapObjectVerify() {
     case JS_MODULE_NAMESPACE_TYPE:
       JSModuleNamespace::cast(this)->JSModuleNamespaceVerify();
       break;
+    case JS_FIXED_ARRAY_ITERATOR_TYPE:
+      JSFixedArrayIterator::cast(this)->JSFixedArrayIteratorVerify();
+      break;
     case JS_SET_TYPE:
       JSSet::cast(this)->JSSetVerify();
       break;
@@ -943,6 +946,16 @@ void JSModuleNamespace::JSModuleNamespaceVerify() {
   module()->ObjectVerify();
 }
 
+void JSFixedArrayIterator::JSFixedArrayIteratorVerify() {
+  CHECK(IsJSFixedArrayIterator());
+
+  CHECK(array()->IsFixedArray());
+  VerifySmiField(kIndexOffset);
+  CHECK(initial_next()->IsJSFunction());
+
+  CHECK_LE(index(), array()->length());
+}
+
 void Module::ModuleVerify() {
   Isolate* isolate = GetIsolate();
   CHECK(IsModule());