ortuno@ can you take a look?

Hrm, looking at the flakiness dasboard:
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=WebAppInstallForceListPolicyTest
the baseline on the builder where it tends to fail seems to be 3..11 seconds.
Then there are a few runs where it times out (capped at 30s).

Could it be that it doesn't time out in these cases because it's slow, but because it's never going to finish?

An example failure could be 
https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8936929877525980416/+/steps/browser_tests__with_patch__on_Windows-10-15063/0/stdout
which looks like this:
[ RUN      ] WebAppInstallForceListPolicyTest.StartUpInstallation
[6864:5528:0828/104153.819:WARNING:discovery_network_list_win.cc(195)] Failed to open Wlan client handle: 1062
[6864:7956:0828/104153.835:WARNING:chrome_browser_main_win.cc(644)] Command line too long for RegisterApplicationRestart:  --brave-new-test-launcher --cfi-diag=0 --disable-gpu-process-for-dx12-vulkan-info-collection --gtest_also_run_disabled_tests --gtest_filter=WebAppInstallForceListPolicyTest.StartUpInstallation --single_process --test-launcher-bot-mode --test-launcher-output="C:\b\s\w\itopvl42\scoped_dir7644_13893\results7644_8244\test_results.xml" --test-launcher-summary-output="C:\b\s\w\ioqxz_ri\output.json" --user-data-dir="C:\b\s\w\itopvl42\scoped_dir7644_13893\d7644_7780" --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 --noerrdialogs --enable-features=TestFeatureForBrowserTest1 --disable-features=NetworkPrediction,SpeculativePreconnect,TestFeatureForBrowserTest2,WebRTC-H264WithOpenH264FFmpeg --disable-gpu-process-for-dx12-vulkan-info-collection --flag-switches-begin --flag-switches-end --file-url-path-alias="/gen=C:\b\s\w\ir\out\Release_x64\gen" --restore-last-session about:blank
[6864:7956:0828/104153.988:WARNING:gaia_auth_fetcher.cc(982)] Could not reach Google Accounts servers: errno -11
[6864:7956:0828/104154.953:WARNING:gaia_auth_fetcher.cc(982)] Could not reach Google Accounts servers: errno -11
[6864:6228:0828/104155.371:WARNING:embedded_test_server.cc(238)] Request not handled. Returning 404: /favicon.ico
[6864:7956:0828/104158.540:WARNING:gaia_auth_fetcher.cc(982)] Could not reach Google Accounts servers: errno -102
[6864:7956:0828/104208.508:WARNING:gaia_auth_fetcher.cc(982)] Could not reach Google Accounts servers: errno -102

OTOH the failure here does not log any gaia_auth_fetcher errors:
https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8936808209894789152/+/steps/browser_tests_on_Windows-10-15063/0/stdout

In short, it's too bad that we only see WARNINGS, and are not really able to know if the test got stuck or if it was really super slow.

Yeah it's possible that we are getting stuck on something. I have a Win10 machine so I should be able to repro and check if its just slowness or if there is actually a problem.

I think that would be cool. But this is not urgent of course :-) Would just be sad to have one test less if it provides value.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a26e58c0ea0c4714d40dde3b0c5db13b93a7780d

commit a26e58c0ea0c4714d40dde3b0c5db13b93a7780d
Author: Giovanni Ortuño Urquidi <ortuno@chromium.org>
Date: Thu Aug 30 12:34:07 2018

policy: Disable flaky WebAppInstallForceListPolicyTest on Windows

The test pushes a policy and then waits for the extension to be
installed. Installing the extension requires loading a website, waiting
for a service worker, parsing the website and finally installing the
app. This takes time but, on Windows, it takes so long that the test
times out.

We have extensive unit tests for all portions of the flow so we could
delete the test and wouldn't loose any coverage, but we just disable
it on Windows since it's the only platforms where the test times out.

Bug: 878797
Change-Id: I12a59e959d8e8dde12c67fac5cb1ce72636bd6ce
Reviewed-on: https://chromium-review.googlesource.com/1195306
Commit-Queue: Giovanni Ortuño Urquidi <ortuno@chromium.org>
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587530}
[modify] https://crrev.com/a26e58c0ea0c4714d40dde3b0c5db13b93a7780d/chrome/browser/policy/policy_browsertest.cc

This is still flaky but we are revisiting the policy. Removing from my queue but marking blocking the launch of the policy.