Benjamin just demonstrated this funky trick for generating pixel
outlines, and as no good deed should go unpunished, I've added his code
to the perf suite.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Provide a hook for the test to be able to compute the number of ops per
second. For instance, the glyphs test uses it to report the number of
kiloglyph per second Cairo is able to render.
