Findit identified the culprit r580365 with confidence 96.7% in the config "chromium.win / Win10 Tests x64"
based on the flakiness trend:

https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVyyAELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKRAWNocm9taXVtLndpbi9XaW4xMCBUZXN0cyB4NjQvMjYxNzYvbmV0d29ya19zZXJ2aWNlX2Jyb3dzZXJfdGVzdHMgb24gV2luZG93cy0xMC0xNTA2My9SWGgwWlc1emFXOXVWMlZpVW1WeGRXVnpkRUZ3YVZSbGMzUXVWMlZpVW1WeGRXVnpkRlJsYzNSUFUwUkUMCxITTWFzdGVyRmxha2VBbmFseXNpcxgBDA

If the culprit above is wrong, please file a bug using this link and hit submit:
https://bugs.chromium.org/p/chromium/issues/entry?status=Unconfirmed&labels=Pri-1,Test-Findit-Wrong&components=Tools%3ETest%3EFindit%3EFlakiness&summary=%5BFindit%5D%20Flake%20Analyzer%20-%20Wrong%20result%20for%20ExtensionWebRequestApiTest.WebRequestTestOSDD&comment=Link%20to%20Analysis%3A%20https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVyyAELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKRAWNocm9taXVtLndpbi9XaW4xMCBUZXN0cyB4NjQvMjYxNzYvbmV0d29ya19zZXJ2aWNlX2Jyb3dzZXJfdGVzdHMgb24gV2luZG93cy0xMC0xNTA2My9SWGgwWlc1emFXOXVWMlZpVW1WeGRXVnpkRUZ3YVZSbGMzUXVWMlZpVW1WeGRXVnpkRlJsYzNSUFUwUkUMCxITTWFzdGVyRmxha2VBbmFseXNpcxgBDA

Automatically posted by the findit-for-me app (https://goo.gl/Ot9f7N).

cduvall@, could you take a look?

Because of the high failure rate, I'm reverting r580365 for now.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ef2b6478296baa49b49aff85eb75a06b5d5a7109

commit ef2b6478296baa49b49aff85eb75a06b5d5a7109
Author: Kunihiko Sakamoto <ksakamoto@chromium.org>
Date: Fri Aug 03 07:22:46 2018

Revert "Fixes ExtensionWebRequestApiTest.WebRequestBlocking with network service"

This reverts commit db56091963b87ed7121cb921a2c31e2922532bfd.

Reason for revert: This made ExtensionWebRequestApiTest.WebRequestTestOSDD flaky.  crbug.com/870588 


Original change's description:
> Fixes ExtensionWebRequestApiTest.WebRequestBlocking with network service
> 
> Getting this test working required a few fixes:
> - Modifying a header rather than Set-Cookie for some tests, which
>   required switching to XMLHttpRequest ( crbug.com/827582 )
> - Handling redirect from http:// -> chrome-extension://, and bypassing
>   security checks if this is from web request
> - Plumbing through whether the request is async or not
> 
> This is not handling subresource redirects because subresource
> redirects to schemes other than http/https/data are not supported
> yet with network service ( crbug.com/868545 ).
> 
> Also adds a bunch of tests for redirects.
> 
> Bug:  721414 
> Cq-Include-Trybots: luci.chromium.try:linux_mojo
> Change-Id: Iabca6e5890b0d5edd066fd8945b19bdbb5d52670
> Reviewed-on: https://chromium-review.googlesource.com/1145956
> Reviewed-by: Nick Carter <nick@chromium.org>
> Reviewed-by: John Abd-El-Malek <jam@chromium.org>
> Reviewed-by: Reilly Grant <reillyg@chromium.org>
> Commit-Queue: Clark DuVall <cduvall@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#580365}

TBR=nick@chromium.org,jam@chromium.org,reillyg@chromium.org,karandeepb@chromium.org,cduvall@chromium.org

Change-Id: Ib831aea7b5afeb6b0e06c79a1d80520d61e02dbf
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug:  721414 , 870588 
Cq-Include-Trybots: luci.chromium.try:linux_mojo
Reviewed-on: https://chromium-review.googlesource.com/1161821
Reviewed-by: Kunihiko Sakamoto <ksakamoto@chromium.org>
Commit-Queue: Kunihiko Sakamoto <ksakamoto@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580467}
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/chrome/browser/chrome_content_browser_client.cc
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/chrome/browser/chrome_content_browser_client.h
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/chrome/browser/extensions/api/web_request/web_request_apitest.cc
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/chrome/test/data/extensions/api_test/webrequest/framework.js
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/chrome/test/data/extensions/api_test/webrequest/test_blocking.js
[delete] https://crrev.com/f20f9a30606d80e1059c2976e73cc99f7de7d76e/chrome/test/data/extensions/api_test/webrequest/test_blocking_cookie.html
[delete] https://crrev.com/f20f9a30606d80e1059c2976e73cc99f7de7d76e/chrome/test/data/extensions/api_test/webrequest/test_blocking_cookie.js
[delete] https://crrev.com/f20f9a30606d80e1059c2976e73cc99f7de7d76e/chrome/test/data/extensions/api_test/webrequest/test_redirects.html
[delete] https://crrev.com/f20f9a30606d80e1059c2976e73cc99f7de7d76e/chrome/test/data/extensions/api_test/webrequest/test_redirects.js
[delete] https://crrev.com/f20f9a30606d80e1059c2976e73cc99f7de7d76e/chrome/test/data/extensions/api_test/webrequest/test_subresource_redirects.html
[delete] https://crrev.com/f20f9a30606d80e1059c2976e73cc99f7de7d76e/chrome/test/data/extensions/api_test/webrequest/test_subresource_redirects.js
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/content/browser/frame_host/render_frame_host_impl.cc
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/content/browser/loader/navigation_url_loader_impl.cc
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/content/browser/loader/navigation_url_loader_impl.h
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/content/browser/storage_partition_impl.cc
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/content/public/browser/BUILD.gn
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/content/public/browser/content_browser_client.cc
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/content/public/browser/content_browser_client.h
[delete] https://crrev.com/f20f9a30606d80e1059c2976e73cc99f7de7d76e/content/public/browser/redirect_checker.h
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/extensions/browser/api/web_request/web_request_api.cc
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/extensions/browser/api/web_request/web_request_api.h
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/extensions/browser/api/web_request/web_request_info.cc
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/extensions/browser/api/web_request/web_request_info.h
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/extensions/browser/api/web_request/web_request_proxying_url_loader_factory.cc
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/extensions/browser/api/web_request/web_request_proxying_url_loader_factory.h
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/extensions/browser/api/web_request/web_request_proxying_websocket.cc
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/extensions/shell/browser/shell_content_browser_client.cc
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/extensions/shell/browser/shell_content_browser_client.h
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/testing/buildbot/filters/mojo.fyi.network_browser_tests.filter
[modify] https://crrev.com/ef2b6478296baa49b49aff85eb75a06b5d5a7109/testing/buildbot/filters/mojo.fyi.network_content_browsertests.filter

Findit identified the culprit r580365 with confidence 76.7% in the config "chromium.win / Win 7 Tests x64 (1)"
based on the flakiness trend:

https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVyuAELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKBAWNocm9taXVtLndpbi9XaW4gNyBUZXN0cyB4NjQgKDEpLzQxNDcxL25ldHdvcmtfc2VydmljZV9icm93c2VyX3Rlc3RzL1JYaDBaVzV6YVc5dVYyVmlVbVZ4ZFdWemRFRndhVlJsYzNRdVYyVmlVbVZ4ZFdWemRGUmxjM1JQVTBSRQwLEhNNYXN0ZXJGbGFrZUFuYWx5c2lzGAEM

If the culprit above is wrong, please file a bug using this link and hit submit:
https://bugs.chromium.org/p/chromium/issues/entry?status=Unconfirmed&labels=Pri-1,Test-Findit-Wrong&components=Tools%3ETest%3EFindit%3EFlakiness&summary=%5BFindit%5D%20Flake%20Analyzer%20-%20Wrong%20result%20for%20ExtensionWebRequestApiTest.WebRequestTestOSDD&comment=Link%20to%20Analysis%3A%20https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVyuAELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKBAWNocm9taXVtLndpbi9XaW4gNyBUZXN0cyB4NjQgKDEpLzQxNDcxL25ldHdvcmtfc2VydmljZV9icm93c2VyX3Rlc3RzL1JYaDBaVzV6YVc5dVYyVmlVbVZ4ZFdWemRFRndhVlJsYzNRdVYyVmlVbVZ4ZFdWemRGUmxjM1JQVTBSRQwLEhNNYXN0ZXJGbGFrZUFuYWx5c2lzGAEM

Automatically posted by the findit-for-me app (https://goo.gl/Ot9f7N).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/17a92a4bc2a9022f80c9516a01a5179c4b2ab07a

commit 17a92a4bc2a9022f80c9516a01a5179c4b2ab07a
Author: Clark DuVall <cduvall@chromium.org>
Date: Fri Aug 24 17:33:34 2018

Fix flaky ExtensionWebRequestApiTest.WebRequestTestOSDD with network service

This test uses an OSDD URL that gives a 404, so allow http errors for
the SimpleURLLoader. It looks like this could flake if there was a delay
between OnReceiveResponse and OnComplete.

Bug:  870588 
Cq-Include-Trybots: luci.chromium.try:linux_mojo
Change-Id: I101894bba7c31fcc7a686ab79b6e6bb936c4c26c
Reviewed-on: https://chromium-review.googlesource.com/1187667
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585894}
[modify] https://crrev.com/17a92a4bc2a9022f80c9516a01a5179c4b2ab07a/components/search_engines/template_url_fetcher.cc
[modify] https://crrev.com/17a92a4bc2a9022f80c9516a01a5179c4b2ab07a/testing/buildbot/filters/mojo.fyi.network_browser_tests.filter