Fix point count computation in tessellating path renderer.

The conic, quadratic and cubic computations were using tolerance^2
instead of tolerance when computing maximum point count, causing paths
to be undertessellated when magnifying and overtessellated when minifying.

(Funny story: this bug went unnoticed back when we were tessellating
paths in screen space, when tolerance and its square were both 1.)

BUG=skia:3731

Review URL: https://codereview.chromium.org/1095773003
1 file changed