Findit identified the culprit r583177 with confidence 70.0% in the config "chromium.linux / Linux Tests (dbg)(1)"
based on the flakiness trend:

https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVytwELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKAAWNocm9taXVtLmxpbnV4L0xpbnV4IFRlc3RzIChkYmcpKDEpLzczNzkyL2Jyb3dzZXJfdGVzdHMvVkdGaVRXRnVZV2RsY2xSbGMzUXVVSEp2WVdOMGFYWmxSbUZ6ZEZOb2RYUmtiM2R1VjJsMGFGVnViRzloWkVoaGJtUnNaWEk9DAsSE01hc3RlckZsYWtlQW5hbHlzaXMYAQw

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%20TabManagerTest.ProactiveFastShutdownWithUnloadHandler&comment=Link%20to%20Analysis%3A%20https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVytwELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKAAWNocm9taXVtLmxpbnV4L0xpbnV4IFRlc3RzIChkYmcpKDEpLzczNzkyL2Jyb3dzZXJfdGVzdHMvVkdGaVRXRnVZV2RsY2xSbGMzUXVVSEp2WVdOMGFYWmxSbUZ6ZEZOb2RYUmtiM2R1VjJsMGFGVnViRzloWkVoaGJtUnNaWEk9DAsSE01hc3RlckZsYWtlQW5hbHlzaXMYAQw

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

fdoray@: coudl you triage.

Findit identified the culprit r583220 with confidence 70.0% in the config "chromium.memory / Linux ASan Tests (sandboxed)"
based on the flakiness trend:

https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVywAELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKJAWNocm9taXVtLm1lbW9yeS9MaW51eCBBU2FuIFRlc3RzIChzYW5kYm94ZWQpLzQ5NzAzL2Jyb3dzZXJfdGVzdHMvVkdGaVRXRnVZV2RsY2xSbGMzUXVVSEp2WVdOMGFYWmxSbUZ6ZEZOb2RYUmtiM2R1VjJsMGFGVnViRzloWkVoaGJtUnNaWEk9DAsSE01hc3RlckZsYWtlQW5hbHlzaXMYAQw

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%20TabManagerTest.ProactiveFastShutdownWithUnloadHandler&comment=Link%20to%20Analysis%3A%20https://findit-for-me.appspot.com/waterfall/flake?key=ag9zfmZpbmRpdC1mb3ItbWVywAELEhdNYXN0ZXJGbGFrZUFuYWx5c2lzUm9vdCKJAWNocm9taXVtLm1lbW9yeS9MaW51eCBBU2FuIFRlc3RzIChzYW5kYm94ZWQpLzQ5NzAzL2Jyb3dzZXJfdGVzdHMvVkdGaVRXRnVZV2RsY2xSbGMzUXVVSEp2WVdOMGFYWmxSbUZ6ZEZOb2RYUmtiM2R1VjJsMGFGVnViRzloWkVoaGJtUnNaWEk9DAsSE01hc3RlckZsYWtlQW5hbHlzaXMYAQw

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

Example failure pasted below, I think this is probably because r583220 enhanced an existing race in the logic that test exercises (@tab manager folks : this change should merely make it so the loop quits immediately when the QuitClosure() is invoked as opposed to a deferred-quit which runs the queue for a few more cycles) :

@fdoray : can we disable this test until we figure this out? Or is it crucial enough to justify reverting r583220 again? (we'd rather not)

[ RUN      ] TabManagerTest.ProactiveFastShutdownWithUnloadHandler
Xlib:  extension "RANDR" missing on display ":99".
[10255:10255:0816/095530.346506:ERROR:browser_dm_token_storage_linux.cc(93)] Error: /etc/machine-id contains 32 characters (32 were expected).
[10255:10290:0816/095530.674416:ERROR:bus.cc(394)] Failed to connect to the bus: Could not parse server address: Unknown address type (examples of valid types are "tcp" and on UNIX "unix")
[10255:10255:0816/095530.713533:WARNING:password_store_factory.cc(253)] Using basic (unencrypted) store for password storage. See https://chromium.googlesource.com/chromium/src/+/master/docs/linux_password_storage.md for more information about password storage options.

(browser_tests:10255): LIBDBUSMENU-GLIB-WARNING **: Unable to get session bus: Unknown or unsupported transport 'disabled' for address 'disabled:'
[10255:10255:0816/095531.235330:WARNING:gaia_auth_fetcher.cc(926)] Could not reach Google Accounts servers: errno -11
../../chrome/browser/resource_coordinator/tab_manager_browsertest.cc:897: Failure
Value of: tab_manager()->DiscardTabImpl(DiscardReason::kProactive)
  Actual: false
Expected: true
Stack trace:
    #0 0x00000cfbf99c in StackTraceGetter::CurrentStackTrace(int, int) ./../../third_party/googletest/custom/gtest/internal/custom/stack_trace_getter.cc:22:27
    #1 0x00000cfe2a80 in testing::internal::UnitTestImpl::CurrentOsStackTraceExceptTop(int) ./../../third_party/googletest/src/googletest/src/gtest.cc:825:35
    #2 0x00000cfe15f7 in testing::internal::AssertHelper::operator=(testing::Message const&) const ./../../third_party/googletest/src/googletest/src/gtest.cc:401:25
    #3 0x000009f96d20 in resource_coordinator::TabManagerTest_ProactiveFastShutdownWithUnloadHandler_Test::RunTestOnMainThread() ./../../chrome/browser/resource_coordinator/tab_manager_browsertest.cc:897:3
    #4 0x000017f38b47 in content::BrowserTestBase::ProxyRunTestOnMainThreadLoop() ./../../content/public/test/browser_test_base.cc:406:5
    #5 0x000016b3e74e in Run ./../../base/callback.h:129:12
    #6 0x000016b3e74e in ChromeBrowserMainParts::PreMainMessageLoopRunImpl() ./../../chrome/browser/chrome_browser_main.cc:2000:0
    #7 0x000016b3b61c in ChromeBrowserMainParts::PreMainMessageLoopRun() ./../../chrome/browser/chrome_browser_main.cc:1384:18
    #8 0x000010634cd5 in content::BrowserMainLoop::PreMainMessageLoopRun() ./../../content/browser/browser_main_loop.cc:1023:13
    #9 0x00001196b2bc in Run ./../../base/callback.h:129:12
    #10 0x00001196b2bc in content::StartupTaskRunner::RunAllTasksNow() ./../../content/browser/startup_task_runner.cc:43:0
    #11 0x00001063063c in content::BrowserMainLoop::CreateStartupTasks() ./../../content/browser/browser_main_loop.cc:934:25
    #12 0x00001063e5d7 in content::BrowserMainRunnerImpl::Initialize(content::MainFunctionParams const&) ./../../content/browser/browser_main_runner_impl.cc:141:15
    #13 0x000010628d9d in content::BrowserMain(content::MainFunctionParams const&) ./../../content/browser/browser_main.cc:43:32
    #14 0x00001601b5fc in RunBrowserProcessMain ./../../content/app/content_main_runner_impl.cc:536:10
    #15 0x00001601b5fc in content::ContentMainRunnerImpl::Run(bool) ./../../content/app/content_main_runner_impl.cc:888:0
    #16 0x00001dc0e679 in service_manager::Main(service_manager::MainParams const&) ./../../services/service_manager/embedder/main.cc:472:29
    #17 0x000016016460 in content::ContentMain(content::ContentMainParams const&) ./../../content/app/content_main.cc:19:10
    #18 0x000017f3767b in content::BrowserTestBase::SetUp() ./../../content/public/test/browser_test_base.cc:322:3

[10255:10255:0816/095532.195033:FATAL:tab_lifecycle_unit.cc(871)] Check failed: IsValidStateChange(last_state, GetState(), reason). Cannot transition TabLifecycleUnit state from LifecycleUnitState::ACTIVE to LifecycleUnitState::FROZEN with reason LifecycleUnitStateChangeReason::RENDERER_INITIATED
    #0 0x00000883a721 in __interceptor_backtrace /b/swarming/w/ir/kitchen-workdir/src/third_party/llvm/compiler-rt/lib/asan/../sanitizer_common/sanitizer_common_interceptors.inc:4024:13
    #1 0x0000168a2e1c in base::debug::StackTrace::StackTrace(unsigned long) ./../../base/debug/stack_trace_posix.cc:808:41
    #2 0x00001660a0b3 in logging::LogMessage::~LogMessage() ./../../base/logging.cc:599:29
    #3 0x0000174e4f78 in resource_coordinator::TabLifecycleUnitSource::TabLifecycleUnit::OnLifecycleUnitStateChanged(mojom::LifecycleUnitState, mojom::LifecycleUnitStateChangeReason) ./../../chrome/browser/resource_coordinator/tab_lifecycle_unit.cc:871:3
    #4 0x0000174e8b95 in resource_coordinator::LifecycleUnitBase::SetState(mojom::LifecycleUnitState, mojom::LifecycleUnitStateChangeReason) ./../../chrome/browser/resource_coordinator/lifecycle_unit_base.cc:77:3
    #5 0x0000174df599 in resource_coordinator::TabLifecycleUnitSource::TabLifecycleUnit::UpdateLifecycleState(resource_coordinator::mojom::LifecycleState) ./../../chrome/browser/resource_coordinator/tab_lifecycle_unit.cc:343:11
    #6 0x000009f96f1d in SimulateFreezeSignal ./../../chrome/browser/resource_coordinator/tab_manager_browsertest.cc:280:11
    #7 0x000009f96f1d in resource_coordinator::TabManagerTest_ProactiveFastShutdownWithUnloadHandler_Test::RunTestOnMainThread() ./../../chrome/browser/resource_coordinator/tab_manager_browsertest.cc:898:0
    #8 0x000017f38b47 in content::BrowserTestBase::ProxyRunTestOnMainThreadLoop() ./../../content/public/test/browser_test_base.cc:406:5
    #9 0x000016b3e74e in Run ./../../base/callback.h:129:12
    #10 0x000016b3e74e in ChromeBrowserMainParts::PreMainMessageLoopRunImpl() ./../../chrome/browser/chrome_browser_main.cc:2000:0
    #11 0x000016b3b61c in ChromeBrowserMainParts::PreMainMessageLoopRun() ./../../chrome/browser/chrome_browser_main.cc:1384:18
    #12 0x000010634cd5 in content::BrowserMainLoop::PreMainMessageLoopRun() ./../../content/browser/browser_main_loop.cc:1023:13
    #13 0x00001196b2bc in Run ./../../base/callback.h:129:12
    #14 0x00001196b2bc in content::StartupTaskRunner::RunAllTasksNow() ./../../content/browser/startup_task_runner.cc:43:0
    #15 0x00001063063c in content::BrowserMainLoop::CreateStartupTasks() ./../../content/browser/browser_main_loop.cc:934:25
    #16 0x00001063e5d7 in content::BrowserMainRunnerImpl::Initialize(content::MainFunctionParams const&) ./../../content/browser/browser_main_runner_impl.cc:141:15
    #17 0x000010628d9d in content::BrowserMain(content::MainFunctionParams const&) ./../../content/browser/browser_main.cc:43:32
    #18 0x00001601b5fc in RunBrowserProcessMain ./../../content/app/content_main_runner_impl.cc:536:10
    #19 0x00001601b5fc in content::ContentMainRunnerImpl::Run(bool) ./../../content/app/content_main_runner_impl.cc:888:0
    #20 0x00001dc0e679 in service_manager::Main(service_manager::MainParams const&) ./../../services/service_manager/embedder/main.cc:472:29
    #21 0x000016016460 in content::ContentMain(content::ContentMainParams const&) ./../../content/app/content_main.cc:19:10
    #22 0x000017f3767b in content::BrowserTestBase::SetUp() ./../../content/public/test/browser_test_base.cc:322:3
    #23 0x0000169994bf in InProcessBrowserTest::SetUp() ./../../chrome/test/base/in_process_browser_test.cc:251:20
    #24 0x00000cff8013 in testing::Test::Run() ./../../third_party/googletest/src/googletest/src/gtest.cc:0:0
    #25 0x00000cffa3d5 in testing::TestInfo::Run() ./../../third_party/googletest/src/googletest/src/gtest.cc:2682:11
    #26 0x00000cffb7e7 in testing::TestCase::Run() ./../../third_party/googletest/src/googletest/src/gtest.cc:2800:28
    #27 0x00000d021327 in testing::internal::UnitTestImpl::RunAllTests() ./../../third_party/googletest/src/googletest/src/gtest.cc:5124:43
    #28 0x00000d020553 in testing::UnitTest::Run() ./../../third_party/googletest/src/googletest/src/gtest.cc:0:0
    #29 0x0000169ed398 in RUN_ALL_TESTS ./../../third_party/googletest/src/googletest/include/gtest/gtest.h:2331:46
    #30 0x0000169ed398 in base::TestSuite::Run() ./../../base/test/test_suite.cc:277:0
    #31 0x00001658dd4e in ChromeTestSuiteRunner::RunTestSuite(int, char**) ./../../chrome/test/base/chrome_test_launcher.cc:65:38
    #32 0x000017fd35bc in content::LaunchTests(content::TestLauncherDelegate*, unsigned long, int, char**) ./../../content/public/test/test_launcher.cc:645:31
    #33 0x00001658eb0b in LaunchChromeTests(unsigned long, content::TestLauncherDelegate*, int, char**) ./../../chrome/test/base/chrome_test_launcher.cc:170:10
    #34 0x00001658d7cc in main ./../../chrome/test/base/browser_tests_main.cc:36:10
    #35 0x7fbdd464af45 in __libc_start_main /build/eglibc-ripdx6/eglibc-2.19/csu/libc-start.c:287:0
    #36 0x0000087ed02a in _start ??:0:0

Cannot upload crash dump: failed to open
[10285:10285:0816/095532.477391:WARNING:x11_util.cc(1391)] X error received: serial 170, error_code 3 (BadWindow), request_code 4, minor_code 0 (Unknown)
[1/1] TabManagerTest.ProactiveFastShutdownWithUnloadHandler (CRASHED)

gab@: there is also https://bugs.chromium.org/p/chromium/issues/detail?id=874958 with a test from the same suite. Hope that it's ok to disable these tests temporarily rather than revert.