A lot of sync integration tests are flaky on Win10:
failures:
TwoClientSessionsSyncTest.DeleteIdleSession
MigrationSingleClientTest.AllTypesWithNigoriAtOnce
SingleClientPollingSyncTest.PRE_ShouldPollWhenIntervalExpiredAcrossRestarts
MigrationSingleClientTest.PrefsOnlyModifyPref
SingleClientUserEventsSyncTest.Encryption
SingleClientSessionsSyncTest.OpenNewWindow
MigrationSingleClientTest.AllTypesAtOnce
TwoClientSessionsSyncTest.SingleClientChanged_E2ETest
SingleClientSessionsSyncTest.FragmentURLNavigation
TwoClientPollingSyncTest.ShouldPollOnStartup
MigrationSingleClientTest.BookmarksPrefsBoth
SingleClientSessionsSyncTest.SourceTabIDSet
MigrationSingleClientTest.PrefsOnlyTriggerNotification
SingleClientSessionsSyncTest.NavigateThenCloseTab
SingleClientPollingSyncTest.ShouldUpdatePollPrefs
MigrationSingleClientTest.BookmarksPrefsIndividually
MigrationTwoClientTest.MigratePrefsAndBookmarksThenModifyBookmark
TwoClientSessionsSyncTest.SingleClientEnabledEncryptionAndChanged
SingleClientSessionsSyncTest.ResponseCodeIsPreserved
MigrationSingleClientTest.AllTypesAtOnceTriggerNotification
SingleClientSessionsSyncTest.TabMovedToOtherWindow
TwoClientSessionsSyncTest.DeleteActiveSession
TwoClientSessionsSyncTest.AllChanged_E2ETest
SingleClientSessionsSyncTest.TimestampMatchesHistory
SingleClientSessionsSyncTest.NavigationChainForwardBack
TwoClientSessionsSyncTest.BothChanged
MigrationTwoClientTest.MigratePrefsThenModifyBookmark
SingleClientSessionsSyncTest.OpenNewTab
TwoClientSessionsSyncTest.SingleClientClosed
SingleClientSessionsSyncTest.NavigationChainAlteredDestructively
... 6 more (36 total) ...

See builds
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Win10%20Tests%20x64%20%28dbg%29/4582
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Win10%20Tests%20x64%20%28dbg%29/4578
https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Win10%20Tests%20x64%20%28dbg%29/4577


Here is a suspicious stack trace that comes up in a lot of those failing tests:
[7380:1164:1130/001550.860:8888796:WARNING:loopback_server.cc(700)] Loopback sync persistent state file does not exist.
[7380:1164:1130/001551.123:WARNING:chrome_browser_main_win.cc(647)] Command line too long for RegisterApplicationRestart:  --cfi-diag=0 --disable-gpu-process-for-dx12-vulkan-info-collection --gtest_also_run_disabled_tests --gtest_filter=SingleClientSessionsSyncTest.NavigateThenCloseTab --single_process --test-launcher-bot-mode --test-launcher-output="C:\b\s\w\itlwwvhu\scoped_dir5912_17910\results5912_14024\test_results.xml" --test-launcher-summary-output="C:\b\s\w\iox28ec3\output.json" --user-data-dir="C:\b\s\w\itlwwvhu\scoped_dir5912_17910\d5912_17385" --disable-offline-auto-reload --disable-background-networking --sync-short-initial-retry-override --sync-short-nudge-delay-for-test --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 --browser-test --ipc-connection-timeout=45 --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=TestFeatureForBrowserTest2 --disable-gpu-process-for-dx12-vulkan-info-collection --flag-switches-begin --flag-switches-end --restore-last-session about:blank
[6308:2628:1130/001551.164:ERROR:direct_composition_surface_win.cc(1477)] EGL_ANGLE_flexible_surface_compatibility not supported
[7380:4280:1130/001551.437:WARNING:discovery_network_list_win.cc(195)] Failed to open Wlan client handle: 1062
[7380:4164:1130/001551.504:ERROR:service_manager_context.cc(286)] Attempting to run unsupported native service: C:\b\s\w\ir\out\Debug_x64\chrome_renderer.service.exe
[7380:4164:1130/001551.508:ERROR:service_manager_context.cc(286)] Attempting to run unsupported native service: C:\b\s\w\ir\out\Debug_x64\chrome_renderer.service.exe
[7380:1164:1130/001551.562:WARNING:gaia_auth_fetcher.cc(891)] Could not reach Google Accounts servers: errno -11
[7380:7720:1130/001552.064:WARNING:sync_encryption_handler_impl.cc(1080)] Nigori had empty encryption keybag.
[7380:7720:1130/001552.069:WARNING:sync_encryption_handler_impl.cc(1080)] Nigori had empty encryption keybag.
[7380:1164:1130/001552.090:INFO:profile_sync_service.cc(2036)] ConfigureDataTypeManager not invoked because datatypes cannot be configured now
[7380:1164:1130/001552.132:ERROR:account_tracker.cc(264)] OnOAuthError
[7380:1164:1130/001552.133:WARNING:account_tracker.cc(190)] Failed to get UserInfo for gaia_id_for_user_gmail.com
[7380:4164:1130/001552.404:ERROR:service_manager_context.cc(286)] Attempting to run unsupported native service: C:\b\s\w\ir\out\Debug_x64\chrome_renderer.service.exe