Don't start pageload right after profiler is started

[sefeng211]

This is a profile I collected by using browsertime: https://perfht.ml/346daRd
The problem is there's no gap between the empty buffer and the page starts to load.

I'd suggest we wait a second after this line

browsertime/lib/firefox/webdriver/firefoxDelegate.js

Line 73 in e37e3b0

await runner.runPrivilegedScript(script, 'Start GeckoProfiler');

[ncalexan]

This is a profile I collected by using browsertime: https://perfht.ml/346daRd
The problem is there's no gap between the empty buffer and the page starts to load.

Why is a gap necessary? Is starting the Gecko profiler not synchronous, meaning that after starting (via privileged JS, say) we still need to wait for it to be ready?

I'd suggest we wait a second after this line

browsertime/lib/firefox/webdriver/firefoxDelegate.js

Line 73 in e37e3b0

await runner.runPrivilegedScript(script, 'Start GeckoProfiler');

Is there some event that tells us the profiler is ready? 1s seems arbitrary.