Await pending directory change in filebrowser model.

[ian-r-rose]

Possible fix for #4009.

[ian-r-rose]

@timkpaine For posterity, can you comment on whether this fixes the issue?

I am not completely convinced that there is no way to generate a race condition after this fix, since there is some subtle logic involving scheduling auto-refreshes of the file browser model (which are not awaited). However, I think this should at least address one class of race condition.

[timkpaine]

@ian-r-rose sure, this seems to fix the particular issue of when you specify a default_url pointing to something like /lab/tree/path/to/dir, where that dir has <<< # of files of the top level dir. Previously, the initial listing of the top level dir came back after the subdirectories, and clobbered the file browser (while leaving the launcher pointing to the subdir).

[timkpaine]

@ian-r-rose this should also resolve the race condition of cd ing between directories quicker than they can be fetched and ending up in the wrong one. (though as you said, this may also have bad interplay with the auto refresh cds).

[ian-r-rose]

I think cding into multiple directories should work okay, since those should be properly awaited or handled in a Promise resolver. I believe the problem here is in the initial refresh() called upon construction of the file browser model, which is not awaited.

I'm trying to construct a test that will catch this, but it's fiddly stuff.

[blink1073]

(a)waiting for Godot...

[ian-r-rose]

Okay, this now has a kind-of-confusing test for the race condition.

[blink1073]

Thanks!

[blink1073]

@meeseeksdev, backport to 0.34.x