[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 75320677c557e18bce4085eef8e3793614623ce0..525c226edadf470303ad9d8049c63eded77ccf1f 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;
@@ -927,6 +930,15 @@ void JSModuleNamespace::JSModuleNamespaceVerify() {
   module()->ObjectVerify();
 }
 
+void JSFixedArrayIterator::JSFixedArrayIteratorVerify() {
+  CHECK(IsJSFixedArrayIterator());
+  CHECK(next()->IsJSFunction());
+  CHECK(array()->IsFixedArray());
+  VerifySmiField(kIndexOffset);
+
+  CHECK_LE(index(), array()->length());
+}
+
 void Module::ModuleVerify() {
   Isolate* isolate = GetIsolate();
   CHECK(IsModule());