Via the flakiness dashboard, here's a more recent failure:
https://logs.chromium.org/v/?s=chromium%2Fbb%2Fchromium.win%2FWin_7_Tests_x64__1_%2F35617%2F%2B%2Frecipes%2Fsteps%2Finteractive_ui_tests%2F0%2Flogs%2FOmniboxViewTest.SelectAllStaysAfterUpdate%2F0

[ RUN      ] OmniboxViewTest.SelectAllStaysAfterUpdate
[1944:1900:0309/105806.242:WARNING:discovery_network_list_win.cc(195)] Failed to open Wlan client handle: 1062
[1944:3288:0309/105806.257:WARNING:chrome_browser_main_win.cc(630)] Command line too long for RegisterApplicationRestart:  --brave-new-test-launcher --cfi-diag=0 --gtest_also_run_disabled_tests --gtest_filter=OmniboxViewTest.SelectAllStaysAfterUpdate --single_process --snapshot-output-dir="e:\b\swarm_slave\w\ioyavvlr" --test-launcher-bot-mode --test-launcher-output="C:\Users\CHROME~2\AppData\Local\Temp\scoped_dir1132_10380\results1132_15605\test_results.xml" --test-launcher-summary-output="e:\b\swarm_slave\w\ioyavvlr\output.json" --user-data-dir="C:\Users\CHROME~2\AppData\Local\Temp\scoped_dir1132_10380\d1132_28800" --disable-offline-auto-reload --no-first-run --no-default-browser-check --enable-logging=stderr --disable-default-apps --wm-window-animations-disabled --disable-component-update --test-type=browser --force-color-profile=srgb --disable-zero-browsers-open-for-tests --ipc-connection-timeout=30 --allow-file-access-from-files --dom-automation --log-gpu-control-list-decisions --disable-backgrounding-occluded-windows --disable-gl-drawing-for-tests --override-use-software-gl-for-tests --force-color-profile=srgb --disable-compositor-ukm-for-tests --enable-features=TestFeatureForBrowserTest1 --disable-features=NetworkPrediction,TestFeatureForBrowserTest2 --flag-switches-begin --flag-switches-end --restore-last-session about:blank
../../chrome/browser/ui/omnibox/omnibox_view_browsertest.cc(1975): error: Expected equality of these values:
  2u
    Which is: 2
  GetSelectionSize(omnibox_view)
    Which is: 0
../../chrome/browser/ui/omnibox/omnibox_view_browsertest.cc(1976): error: Value of: omnibox_view->IsSelectAll()
  Actual: false
Expected: true
../../chrome/browser/ui/omnibox/omnibox_view_browsertest.cc(1983): error: Expected equality of these values:
  2u
    Which is: 2
  GetSelectionSize(omnibox_view)
    Which is: 0
../../chrome/browser/ui/omnibox/omnibox_view_browsertest.cc(1987): error: Expected equality of these values:
  1u
    Which is: 1
  GetSelectionSize(omnibox_view)
    Which is: 0
../../chrome/browser/ui/omnibox/omnibox_view_browsertest.cc(2000): error: Expected equality of these values:
  2u
    Which is: 2
  GetSelectionSize(omnibox_view)
    Which is: 0
../../chrome/browser/ui/omnibox/omnibox_view_browsertest.cc(2004): error: Expected equality of these values:
  1u
    Which is: 1
  GetSelectionSize(omnibox_view)
    Which is: 0
[  FAILED  ] OmniboxViewTest.SelectAllStaysAfterUpdate, where TypeParam =  and GetParam() =  (1606 ms)

Tommy,

This was seemingly first reported right after you submitted
https://chromium-review.googlesource.com/c/chromium/src/+/944508
which deals with selection in the omnibox.

Even if that's not the cause, it's clear you're familiar with this area.  Can you please take a look?

thanks,
mark

P.S.  The first error (line 1975) is the main one; the rest I think are downstream effects of that failure (1976, 1983, 1987) or re-testing the same thing that was the earlier failure (2000) and the downstream effect of that failure (2004).

Sure, thanks mark.

Still seeing flakes on the CQ today : https://logs.chromium.org/v/?s=chromium%2Fbb%2Ftryserver.chromium.win%2Fwin7_chromium_rel_ng%2F149471%2F%2B%2Frecipes%2Fsteps%2Finteractive_ui_tests__with_patch_%2F0%2Flogs%2FOmniboxViewTest.SelectAllStaysAfterUpdate%2F0

This has been open for a month. What's the status? Flakes slow every dev down and are P1. Please disable this test if not fixing it shortly.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ed9d8eebf5c8fac7a11ff3f9fcb615443a7640a2

commit ed9d8eebf5c8fac7a11ff3f9fcb615443a7640a2
Author: Tommy C. Li <tommycli@chromium.org>
Date: Mon Jul 23 16:54:18 2018

Omnibox: Update a browsertest in an attempt to fix flakiness

Seems like a long shot to fix the flakiness of this browser test, but
this fixes an error anyways.

Bug:  817270 
Change-Id: I97bf32f5924f58e0965c80587eedd419a9739ca1
Reviewed-on: https://chromium-review.googlesource.com/1145863
Commit-Queue: Tommy Li <tommycli@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577189}
[modify] https://crrev.com/ed9d8eebf5c8fac7a11ff3f9fcb615443a7640a2/chrome/browser/ui/omnibox/omnibox_view_browsertest.cc

Hmm maybe that last CL did fix the flakiness. It doesn't look flaky on the dashboard anymore:

https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=interactive_ui_tests&tests=OmniboxViewTest.SelectAllStaysAfterUpdate
https://findit-for-me.appspot.com/ranked-flakes?test_filter=OmniboxViewTest