- populate the widget with addItems(QStringList) instead of
  looping over addItem(QString)
- Use findText() instead of looping over itemText(int).
  QComboBox::findText() delegates searching to the model
  (via QAbstractItemModel::match()), so is potentially
  much faster. I say potentially, because match() isn't
  properly reimplemented in most models, yet. But that is
  something to fix in the models.

Change-Id: I6e52cf5af810ab7869c0270504a241868a5ca281
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>