Add clear benchmark

Bug: skia:
Change-Id: I2cfc365e41942ad7cc3fbdf9b815df6e25b1f36f
Reviewed-on: https://skia-review.googlesource.com/c/160601
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
2 files changed