V1 charts display dates below their minimap, and revision numbers below their main chart.
V2 charts should display dates in a more efficient format below both the main chart and the minimap. Revision numbers will still be available in the tooltip.

The dates may need to be collected from a few different places temporarily:
 * Row.r_timestamp if it exists, as it currently does for fuchsia test suites and will soon for data from chromium.perf bots, 
 * Row.revision if they look like unix timestamps in either seconds or milliseconds,
 * Row.timestamp if the bot is not ChromeOS.

ChromeOS timeseries can continue to display Row.revision numbers in x-axes until they upload revision timestamps.
Eventually, all clients should upload revision timestamps to the indexed property Row.revision, so this logic can be simplified then to just always display Row.revision in an efficient date format.