Perf dashboard doesn’t show the right unit for Safari UI tests

Perf dashboard doesn’t show the right unit for Safari UI tests
https://bugs.webkit.org/show_bug.cgi?id=141238

Reviewed by Darin Adler.

Safari UI tests use custom metrics that end with "Time". This patch teaches the perf dashboard how to
get the unit for a given metric based on the suffix of the metric name instead of hard-coding the mapping
between metrics and their units.

* public/js/helper-classes.js:
(PerfTestRuns): Use the suffix of the metric name to compute the unit.
* public/v2/manifest.js:
(App.Manifest.fetchRunsWithPlatformAndMetric): Ditto. Also set "useSI" property iff for "bytes".
* public/v2/interactive-chart.js:
(App.InteractiveChartComponent._constructGraphIfPossible): Respect useSI. Use toPrecision(3) otherwise.
(App.InteractiveChartComponent._relayoutDataAndAxes): Place the unit vertically on the left of ticks.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@179613 268f45cc-cd09-0410-ab3c-d52691b4dbfc