This failure has bisected down to r511698.

+iclelland@

It's been less than 24h since the CL in #c1 has landed + we are still early in the milestone, so I am considering just reverting the CL to make the bots green again (e.g. the linux_site_isolation trybot which is currently mandatory for *some* CLs + the Site Isolation FYI bots like https://build.chromium.org/p/chromium.fyi/builders/Site%20Isolation%20Linux).

WDYT?

I'd probably revert (I certainly would if I were sheriffing).

If we didn't want to do that, it's also easy to add a flaky expectation to the site isolation tests, but as you say, it's early enough that we should be able to revert, and find and fix the cause of the flake instead.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b2ea20316f9337e8c47eadf0b0385d8c40a1d573

commit b2ea20316f9337e8c47eadf0b0385d8c40a1d573
Author: Łukasz Anforowicz <lukasza@chromium.org>
Date: Thu Oct 26 17:36:14 2017

Revert "Add Feature Policy checks for midi to blink"

This reverts commit ddbfc9bca23fd09a969c04e2a107809da3e2146c.

Reason for revert: This CL caused flaky timeouts linux_site_isolation trybot and on Site Isolation FYI bots - see  https://crbug.com/778709 

Original change's description:
> Add Feature Policy checks for midi to blink
> 
> Currently we check the feature policy for midi in the PermissionService.
> This means that we can't easily return a specific error message for denial due
> to FP. Also, several permission features do not use the PermissionService
> codepath and need to be checked individually anyway, so it seems more
> appropriate to do this for all permissions.
> 
> This CL adds these checks to NavigatorWebMIDI.cpp. It also logs a console
> warning when the feature is disabled to help inform developers.
> Furthermore, a UseCounter counts how many times the feature has been
> blocked due to Feature Policy.
> 
> Bug:  689802 
> Change-Id: I527278323ea9662a29db24f9b35071b901e2b58f
> Reviewed-on: https://chromium-review.googlesource.com/724580
> Commit-Queue: Raymes Khoury <raymes@chromium.org>
> Reviewed-by: Timothy Loh <timloh@chromium.org>
> Reviewed-by: Takashi Toyoshima <toyoshim@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#511698}

TBR=raymes@chromium.org,toyoshim@chromium.org,timloh@chromium.org

Change-Id: I9fa08cbbcb8b02803a2fa6aab9c2e518fd5498f2
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug:  689802 ,  778709 
Reviewed-on: https://chromium-review.googlesource.com/739882
Reviewed-by: Łukasz Anforowicz <lukasza@chromium.org>
Commit-Queue: Łukasz Anforowicz <lukasza@chromium.org>
Cr-Commit-Position: refs/heads/master@{#511865}
[modify] https://crrev.com/b2ea20316f9337e8c47eadf0b0385d8c40a1d573/third_party/WebKit/LayoutTests/VirtualTestSuites
[add] https://crrev.com/b2ea20316f9337e8c47eadf0b0385d8c40a1d573/third_party/WebKit/LayoutTests/virtual/feature-policy-permissions/http/tests/webmidi/README.txt
[modify] https://crrev.com/b2ea20316f9337e8c47eadf0b0385d8c40a1d573/third_party/WebKit/Source/modules/webmidi/NavigatorWebMIDI.cpp
[modify] https://crrev.com/b2ea20316f9337e8c47eadf0b0385d8c40a1d573/third_party/WebKit/public/platform/web_feature.mojom
[modify] https://crrev.com/b2ea20316f9337e8c47eadf0b0385d8c40a1d573/tools/metrics/histograms/enums.xml

The bots is green since https://build.chromium.org/p/chromium.fyi/builders/Site%20Isolation%20Linux/builds/22004 (which included the revert from #c4).