Scale extra CPUs to powersave during nanobench.

This scaling logic correctly accounts for some devices
which have multiple CPUs.  Previously, we were scaling
the smaller of these CPUs, which likely had a negative
impact on nanobench, given nanobench was single threaded
and the CPUs weren't allowed to idle much (because we
set the CPU).

This CL sets those additional CPUs to powersave when we run
nanobench and then correctly scales down the beefier
CPU we want to run nanobench on.

For DM, we just run it in ondemand mode, which will
hopefully be "as fast as possible", but allow the CPU
governor to scale down if overheating becomes a problem.

Bug: skia:7378
notry=TRUE
Change-Id: I45ca5d9fb32182233d1b2d094842c879f2b84da4
Reviewed-on: https://skia-review.googlesource.com/83240
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
33 files changed