Benchmark Breakdown from multiple phases

[Jigao Luo]

(I mentioned this topic in https://github.com/google/benchmark/issues/1140 before I found this channel.)

In principle, I would like to time multiple stages (e.g. build, lookup of an index) then to observe and plot a breakdown figure to check, if build **and** probe are performant enough. Somehow the build stage and lookup stage of an index is highly correlated.

Is that we don't support such feature? Is a plan to include this feature in the future release?

I would say a breakdown plot is essential in benchmarking :D.