Add HardStopGradientBench_ScaleNumHardStops.cpp

Rename HardStopGradientBench.cpp to HardStopGradientBench_ScaleNumColors.cpp

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2178913003

Review-Url: https://codereview.chromium.org/2178913003
3 files changed