The current approach to adjust the icon size of dash items is rather
expensive: the size of each item is changed from largest to smallest,
until the height of the dash fits the maximum available height, so
quite some ClutterTextures are created and disposed.
A better approach is to calculate the required size beforehand and
only change the icon size when necessary.
https://bugzilla.gnome.org/show_bug.cgi?id=636156