Fix up the clip mask manager's creation of paths (w.r.t. volatility)

I don't expect this to make any difference (perf-wise) but it seems more correct.

This CL relies on https://codereview.chromium.org/1421533007/ (Fix ClipMaskManager's SW-fallback logic)

Review URL: https://codereview.chromium.org/1419403002
2 files changed