LinkedHashMap< K, V>.of constructor
    Creates a LinkedHashMap that contains all key value pairs of other.
Implementation
factory LinkedHashMap.of(Map<K, V> other) =>
    new LinkedHashMap<K, V>()..addAll(other);
    Creates a LinkedHashMap that contains all key value pairs of other.
factory LinkedHashMap.of(Map<K, V> other) =>
    new LinkedHashMap<K, V>()..addAll(other);