[modules] Add internal printer method for JSModuleNamespace.

R=adamk@chromium.org
BUG=v8:1569

Review-Url: https://codereview.chromium.org/2410003002
Cr-Commit-Position: refs/heads/master@{#40181}

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());

src/objects.h

@@ -7881,6 +7881,7 @@ class JSGeneratorObject: public JSObject {
 class JSModuleNamespace : public JSObject {
  public:
   DECLARE_CAST(JSModuleNamespace)
+  DECLARE_PRINTER(JSModuleNamespace)
   DECLARE_VERIFIER(JSModuleNamespace)
 
   // The actual module whose namespace is being represented.