Allow the displayed summary value to be something other than the median?

```
For microbenchmark results, there's a lot to like about the idea of choosing
the 10th or 20th percentile value as the most interesting one to report.

While for users with other kinds of performance test results, they may care
about 90th-percentile latency, or whatever.

I'm roughly imagining being able to open up a list of advanced options on a
benchmark result page, and set the percentile to whatever you want (though I
would probably want a way to make it my default).

```

Original issue reported on code.google.com by `kevinb@google.com` on 31 Jan 2013 at 8:36