Adds descriptions to WebRTC UMA histograms of system delay jumps
Adds descriptions to WebRTC UMA histograms of system delay jumps

The calculations in WebRTC have been committed as https://chromium.googlesource.com/external/webrtc/+/1ca324f23770e17d19433ccd3a3b021870d709ca
Rolled into chromium at https://chromium.googlesource.com/chromium/src/+/c809260cce6b0dbb6b596a5c976020b10fe4a668

For details see the review at https://codereview.webrtc.org/1213733004/

It will be included in the next roll to chromium.

BUG=488124

Review URL: https://codereview.chromium.org/1217483003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#337014}

ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,lihui7115/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend