Enable Skia's edge-antialiasing tessellating path renderer.

This will affect all concave paths rendered in 2D canvas, and in SVG
content with five concave paths or fewer.  SVG content with >5 five paths
will continue to be vetoed to MSAA if available, or software
rasterization if not.

BUG=642376

Review-Url: https://codereview.chromium.org/2680003002
Cr-Commit-Position: refs/heads/master@{#449081}