Make sure that shared rasterizers don't get smaller
Make sure that shared rasterizers don't get smaller

Before this they could get smaller in one dimension while getting larger
in the other.

Bercon/glbrush.js,garg/glbrush.js,garg/glbrush.js,Bercon/glbrush.js,Oletus/glbrush.js,garg/glbrush.js,garg/glbrush.js,Bercon/glbrush.js,Bercon/glbrush.js,Oletus/glbrush.js,Oletus/glbrush.js