Charts of percentage change against baseline

[johnaohara]

Feature idea.

Produce a chart of %change from a baseline, instead of absolute values.

Change charts currently plot absolute measured values as a timeseries.

For releases of minor/revision versions, it is often useful to monitor the percentage change from the release baseline to track changes over time.

Plotting %change instead of absolute values allows multiple metrics to be plotted on the same chart where the absolute values differ in magnitude of scale,

A user could select a baseline metric (i.e. a run that represents a major version first release) and then subsequent runs that are part of the major version release change, the % difference from the baseline (e.g. similar to how experiments currently work) are calculated from the baseline and plotted on a chart instead of the absolut values

See example: https://perf.golang.org/dashboard/