Avoid creating std::function in run_pipeline().

This avoids a malloc/free per SkRasterPipeline::run(), with no downside.

  $ out/nanobench --benchType skcolorcodec --colorImages images/colorspace/201293.jpg --skps noskps --xform_only --srgb --ms 10000

  target:  273µs
  current: 395µs
  this CL: 375µs

CQ_INCLUDE_TRYBOTS=skia.primary:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD

Change-Id: Icd62f505f555ebf4ca66ee77a476f59cab68433d
Reviewed-on: https://skia-review.googlesource.com/5447
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Matt Sarett <msarett@google.com>
1 file changed