HashMap<K, V>.from constructor
Creates a HashMap that contains all key/value pairs of other.
The keys must all be instances of K and the values of V.
The other map itself can have any type.
Implementation
factory HashMap.from(Map other) {
Map<K, V> result = new HashMap<K, V>();
other.forEach((k, v) {
result[k] = v;
});
return result;
}