scope nonDefaultInterfaceMethods

// TODO: convert to regularly cleared normal map
static Map<Class, Method[]> #cache = newDangerousWeakHashMap();

static Method[] nonDefaultInterfaceMethods(Class c) {
  Method[] methods;
  synchronized(cache) {
    methods = cache.get(c);
    if (methods == null)
      cache.put(c, methods = toTypedArray(Method.class, findNonDefaultInterfaceMethods(c)));
  }
  ret methods;
}

Began life as a copy of #1034765