I looked at those between "try run at 2017-03-24 07:51:04 UTC" and "try run at 2017-03-29 14:43:50 UTC".

1 Swarming bot died -- https://chromium-swarm.appspot.com/task?id=3533002dc4fc3010&refresh=10&show_raw=1
4 timeout -- https://chromium-swarm.appspot.com/task?id=3532269888d26310&refresh=10&show_raw=1

As there is not output at all, can't investigate further.

In the chromium-try-flakes link, there are two entries with "
try run at 2017-03-29 14:43:50 UTC". They are duplicate, maybe a bug?

Removed from sheriff queue for now, as it is not actionable.

Re #2, thanks, filed  http://crbug.com/706651 .

Detected 4 new flakes for test/step "ui_base_unittests". To see the actual flakes, please visit https://chromium-try-flakes.appspot.com/all_flake_occurrences?key=ahVzfmNocm9taXVtLXRyeS1mbGFrZXNyHAsSBUZsYWtlIhF1aV9iYXNlX3VuaXR0ZXN0cww. This message was posted automatically by the chromium-try-flakes app. Since flakiness is ongoing, the issue was moved back into Sheriff Bug Queue (unless already there).

-Sheriff-Chromium again

Detected 3 new flakes for test/step "ui_base_unittests". To see the actual flakes, please visit https://chromium-try-flakes.appspot.com/all_flake_occurrences?key=ahVzfmNocm9taXVtLXRyeS1mbGFrZXNyHAsSBUZsYWtlIhF1aV9iYXNlX3VuaXR0ZXN0cww. This message was posted automatically by the chromium-try-flakes app. Since flakiness is ongoing, the issue was moved back into Sheriff Bug Queue (unless already there).

The tests are still timing out with no real output.

Detected 6 new flakes for test/step "ui_base_unittests". To see the actual flakes, please visit https://chromium-try-flakes.appspot.com/all_flake_occurrences?key=ahVzfmNocm9taXVtLXRyeS1mbGFrZXNyHAsSBUZsYWtlIhF1aV9iYXNlX3VuaXR0ZXN0cww. This message was posted automatically by the chromium-try-flakes app. Since flakiness is ongoing, the issue was moved back into Sheriff Bug Queue (unless already there).

Looks specific to iOS. Could a trooper figure out how to get actionable data from one of the bots?

The only data I've got is that majority of timeouts happens on 'iPad Air 2 iOS 10.0' for some reason.

Also it happens with other tests too: https://chromium-swarm.appspot.com/tasklist?c=name&c=state&c=created_ts&c=user&c=bot&et=1494440640000&f=state%3ATIMED_OUT&f=platform%3Asimulator&l=50&n=true&s=created_ts%3Adesc&st=1494354240000

In most cases logs are not very useful:

"""
Device wiped.
/b/s/w/ir/src/out/Debug-iphonesimulator/iossim -d iPad Air 2 -s 10.0 /b/s/w/ir/src/out/Debug-iphonesimulator/url_unittests.app

User defaults from command line:
    IDETestRunSpecificationPath = /var/folders/p4/py6nlvcx4fs5s3fg51_pzqmc0000gm/T/6793337A-5122-48CA-9BF2-1D09F4C7D790

<EOF>
"""

So it seem like iossim is getting stuck?.. I have no idea how it works. I hope Sana or Sergey can debug it further.

"User defaults from command line" suggests iossim successfully started the iOS Simulator, but the iOS Simulator hung with no output.

I'll try to look into it. 

Detected 3 new flakes for test/step "ui_base_unittests". To see the actual flakes, please visit https://chromium-try-flakes.appspot.com/all_flake_occurrences?key=ahVzfmNocm9taXVtLXRyeS1mbGFrZXNyHAsSBUZsYWtlIhF1aV9iYXNlX3VuaXR0ZXN0cww. This message was posted automatically by the chromium-try-flakes app.

Detected 3 new flakes for test/step "ui_base_unittests". To see the actual flakes, please visit https://chromium-try-flakes.appspot.com/all_flake_occurrences?key=ahVzfmNocm9taXVtLXRyeS1mbGFrZXNyHAsSBUZsYWtlIhF1aV9iYXNlX3VuaXR0ZXN0cww. This message was posted automatically by the chromium-try-flakes app.

Indeed, iossim still occasionally gets stuck for 20m and eventually gets killed by swarming.

I don't think it's a trooper issue, but something we should investigate. I'm releasing the bug as I'm not actively working on it, but may come back to it in the future.