Containers example is slow #248
Description
While working on #227 I ran through all of the examples to try to spot layout issues that I was introducing. I discovered this example takes entirely too long to redraw. I did some very quick profiling and sped up font family list handling, but I think the real issue is probably related to how the main branch is now consistently applying font settings to every context. I suspect there's invalidation happening where there shouldn't be.