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

src/gpu/batches/GrTessellatingPathRenderer.cpp

@@ -25,8 +25,6 @@
 
 #include <stdio.h>
 
-#define SK_DISABLE_SCREENSPACE_TESS_AA_PATH_RENDERER
-
 /*
  * This path renderer tessellates the path into triangles using GrTessellator, uploads the
  * triangles to a vertex buffer, and renders them with a single draw call. It can do screenspace