It looks like one of the intentions of the following three methods is to allow callers of them to determine whether or not a class can be unloaded. But if the class is a VM anonymous class then it can be unloaded regardless of its loader.

// Returns true if this class loader data is for the system class loader.
bool ClassLoaderData::is_system_class_loader_data() const {
  return SystemDictionary::is_system_class_loader(class_loader());
}

// Returns true if this class loader data is for the platform class loader.
bool ClassLoaderData::is_platform_class_loader_data() const {
  return SystemDictionary::is_platform_class_loader(class_loader());
}

// Returns true if this class loader data is one of the 3 builtin
// (boot, application/system or platform) class loaders. Note, the
// builtin loaders are not freed by a GC.
bool ClassLoaderData::is_builtin_class_loader_data() const {
  return (is_the_null_class_loader_data() ||
          SystemDictionary::is_system_class_loader(class_loader()) ||
          SystemDictionary::is_platform_class_loader(class_loader()));
}

So, either add checks for anonymous classes to the above methods and/or clarify their comments.