Add hardware monitoring to skpbench

Adds a Hardware class with hooks for entering and exiting
"benchmarking" mode (e.g. locking clocks, etc.) as well as periodic
polling of hardware to verify the environment is stable.

Adds a partial implementation for generic Android hardware, but
ultimately we will need to write specific classes tailored to each
unique platform we need to test.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2360473002

Review-Url: https://codereview.chromium.org/2360473002
7 files changed