[modules] Add internal printer method for JSModuleNamespace.

src/objects-printer.cc

Index: src/objects-printer.cc
diff --git a/src/objects-printer.cc b/src/objects-printer.cc
index 9054371e849c6d9173cc243879b98a5015fc9cab..48182152a374b07b387d103ce690d865519eab66 100644
--- a/src/objects-printer.cc
+++ b/src/objects-printer.cc
@@ -166,6 +166,9 @@ void HeapObject::HeapObjectPrint(std::ostream& os) {  // NOLINT
     case JS_WEAK_SET_TYPE:
       JSWeakSet::cast(this)->JSWeakSetPrint(os);
       break;
+    case JS_MODULE_NAMESPACE_TYPE:
+      JSModuleNamespace::cast(this)->JSModuleNamespacePrint(os);
+      break;
     case FOREIGN_TYPE:
       Foreign::cast(this)->ForeignPrint(os);
       break;
@@ -1168,6 +1171,12 @@ void Module::ModulePrint(std::ostream& os) {  // NOLINT
   os << "\n";
 }
 
+void JSModuleNamespace::JSModuleNamespacePrint(std::ostream& os) {  // NOLINT
+  HeapObject::PrintHeader(os, "JSModuleNamespace");
+  os << "\n - module: " << Brief(module());
+  os << "\n";
+}
+
 void PrototypeInfo::PrototypeInfoPrint(std::ostream& os) {  // NOLINT
   HeapObject::PrintHeader(os, "PrototypeInfo");
   os << "\n - prototype users: " << Brief(prototype_users());