Creates a SplayTreeMap 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.
factory SplayTreeMap.from(Map other,
[int compare(K key1, K key2), bool isValidKey(potentialKey)]) {
SplayTreeMap<K, V> result = new SplayTreeMap<K, V>(compare, isValidKey);
other.forEach((k, v) {
result[k] = v;
});
return result;
}