Enable the screenspace AA tessellating path renderer.

Enable the screenspace AA tessellating path renderer.

This will enable the new path renderer in Skia. It is still disabled
in Chrome, to protect layout test results.

Note: this will cause minor pixel diffs in a number of GMs' GPU results,
including drawregionmodes, dstreadshuffle, smallarc, path-reverse,
bug339297, parsedpaths, zero_control_stroke, strokedlines, smallpaths,
circular_arcs_stroke_round, concavepaths, circular_arcs_stroke_square,
clipcubic, arcto, persp_shaders_aa, complexclip3_complex,
circular_arcs_stroke_and_fill_butt, complexclip_aa,
complexclip_aa_layer, complexclip_aa_invert, complexclip3_simple,
complexclip_aa_layer_invert, shadertext, shadertext2,
convex-lineonly-paths-stroke-and-fill, poly2poly, glyph_pos_h_b,
glyph_pos_h_f, glyph_pos_n_f, and glyph_pos_n_s.

Note: it also "fixes" crbug_640176, or more accurately, hides the
failure, since the default path renderer likely still has the bug.

BUG=642376
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2303743002

Review-Url: https://codereview.chromium.org/2303743002