private static Set<Bitmap.Config> getDefaultAllowedConfigs() {
        Set<Bitmap.Config> configs = new HashSet<Bitmap.Config>();
        configs.addAll(Arrays.asList(Bitmap.Config.values()));
        if (Build.VERSION.SDK_INT >= 19) {
            configs.add(null);
        }
        return Collections.unmodifiableSet(configs);
    }
Constructor for LruBitmapPool.

@param maxSize The initial maximum size of the pool in bytes.
@param allowedConfigs A white listed set of {@link Bitmap.Config} that are allowed to be put
                      into the pool. Configs not in the allowed set will be rejected.
core/src/main/java/com/bumptech/glide/load/engine/bitmap_recycle/LruBitmapPool.java