2ptconical stage

Initial impl, for the well-behaved case (focal point inside).

MBP numbers -

Before:

   3365.87 !	gradient_conical_clamp_shallow	srgb
   3590.88 !	gradient_conical_clamp_shallow_dither	srgb
   3376.91 !	gradient_conical_clamp_3color	srgb
   3351.64 !	gradient_conical_clamp_hicolor	srgb
   3379.35 !	gradient_conical_clamp	srgb

After:

    648.93 !	gradient_conical_clamp_shallow	srgb
    665.12 !	gradient_conical_clamp_shallow_dither	srgb
    773.98 !	gradient_conical_clamp_3color	srgb
   1175.35 !	gradient_conical_clamp_hicolor	srgb
    619.17 !	gradient_conical_clamp	srgb

Change-Id: I07b22a758363e1f340a6041bca53bdef74229eb9
Reviewed-on: https://skia-review.googlesource.com/20906
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Klein <mtklein@chromium.org>
6 files changed