1513265 - panelsInBackground DAMP test do not include async netmonitor work

Status: NEW

(DevTools :: Netmonitor, enhancement, P3)

Description

[Alexandre Poirot [:ochameau]]

Bug 1474843 highlighter that panels in background test was subject to mis-interpretation as we do not include the netmonitor async events, which may endup being running during the test or not, depending on the load.
Thus leading to hard-to-interpret results.

https://searchfox.org/mozilla-central/rev/adcc169dcf58c2e45ba65c4ed5661d666fc3ac74/testing/talos/talos/tests/devtools/addon/content/tests/toolbox/panels-in-background.js#23-27
  // Reload the page and wait for all HTTP requests
  // to finish (1 doc + 600 XHRs).
  let payloadReady = waitForPayload(601, monitor.panelWin);
  await reloadPageAndLog("panelsInBackground", toolbox);
  await payloadReady;

When applying bug 1474843, panelsInBackground was becoming slower whereas the overall time for payloadReady to resolve was the same. It happens that it slightly changes the timings and the netmonitor code actually happens *during* the reloadPageAndLog calls, whereas before, it wasn't. Netmonitor observers were only called *after* reloadPageAndLog resolved.

So I think it would be helpful to use two distinct measurements.
The existing panelsInBackground, which highlights raw page reload performance,
and another one that includes the payloadReady wait.
We might as well try to wait for async work related to the console...