This was deprecated, and removed from ggplot2 2.0.0.

The built-in 'percent' function occasionally produces NaNs when given negative
inputs. It looks like this has been fixed in more recent versions of R, but the
workaround is simple.

In particular, the graphs are useful for analysing JavaScript benchmark results.
JavaScript benchmarks often exhibit bimodal (or otherwise noisy) behaviour, and
take a very long time to run, so simply examining the mean of a set of 10 runs
tends to be misleading. This tool tries to plot every result in a way such that
trends and patterns can be spotted.