base-icon: Enforce the requested icon size

base-icon: Enforce the requested icon size

Mainly due to StTextureCache's way of handling fallback icons, an
implementation of BaseIcon.createIcon() may return an icon smaller
than the requested size. Given that BaseIcon is not used for isolated
elements, but rather for groups of related items (App view, Dash,
Search Results, ...), having some elements end up with the wrong
size is more annoying than having some elements end up ugly due to
scaling, so explicitly enforce the requested icon size.

https://bugzilla.gnome.org/show_bug.cgi?id=642043