We shouldn't create QPixmaps when comparing QBrushes that do not
contain a QPixmap.
This patch extends the comparison logic to comparing QImage cachekeys
if the brushes are QImage based.
Note the comparison still produces false negatives on equal content on
different pixmaps and images, but this is preserving existing behavior.
Task-number: QTBUG-43766
Change-Id: I001b4032172c1e568aad311f7df2eaae6aee8dc6
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>
57469a8e10