This uses the mutator utilization distribution to compute the p99.9,
p99, and p95 mutator utilization topograph lines and display them
along with the MMU.

Change-Id: I8c7e0ec326aa4bc00619ec7562854253f01cc802
Reviewed-on: https://go-review.googlesource.com/c/60800
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>