Adds common helper functions for Running Graphs and Histograms.

Bug: angleproject:4965
Change-Id: I8c7295217c637e377b74b4a336eb151b8a7c9596
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2358518
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>