Ignore fill when stroke & filling convex line-only paths

Ignore fill when stroke & filling convex line-only paths

This seems to work well for miter and bevel joins with the resulting stroke and fill path remaining convex. There seems to be an issue with round joins where the outer generated shell is usually not convex. Without this CL the resulting stroke & filled paths are always concave.

Perf-wise (on Windows):

convex-lineonly-paths-stroke-and-fill bench

(in ms)   w/o   w/CL    %decrease

8888      2.88  2.01      30.2

gpu       4.4   1.38      68.6

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Review-Url: https://codereview.chromium.org/2275243003