4d7ea15ca Roll third_party/benchmark to a779ffce872b4c811beef482e18bd0b63626aa42 (flutter/engine#11492) (#39318)

git@github.com:flutter/engine.git/compare/92c63e848a5e...4d7ea15cae36

git log 92c63e848a5e..4d7ea15cae36 --no-merges --oneline
2019-08-27 chris@bracken.jp Roll third_party/benchmark to a779ffce872b4c811beef482e18bd0b63626aa42 (flutter/engine#11492)


If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/flutter-engine-flutter-autoroll
Please CC garyq@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md