resizeBuffer method
Implementation
void resizeBuffer() {
var newSize = count * 2 + 1;
if (newSize < count) throw Exception('Integer overflow');
final newGroupings = List<Grouping<TKey, TValue>>(newSize);
var g = lastGrouping;
do {
g = g.next;
final index = g.hashCode % newSize;
g.hashNext = newGroupings[index];
newGroupings[index] = g;
} while (g != lastGrouping);
groupings = newGroupings;
}