[6424:4144:0727/152950:14223453:FATAL:test_simple_task_runner.cc(21)] Check failed: thread_checker_.CalledOnValidThread(). 

is the error, but don't have a stack yet.

no symbols in task 3047452fbe0d9310, so can't get stacks.

this looks like it's still happening on every try job

e.g. 

https://build.chromium.org/p/tryserver.chromium.win/builders/win10_chromium_x64_rel_ng/builds/254

but it's passing because it's not a regression from the patch. Would be nice if someone looked at this. Adding a few random people.

Stack from bot:
ExtensionWelcomeNotificationTest.DelayedPreferenceSyncNeverShown (run #1):
[ RUN      ] ExtensionWelcomeNotificationTest.DelayedPreferenceSyncNeverShown
[7852:8368:0812/143923:6472203:FATAL:test_simple_task_runner.cc(21)] Check failed: thread_checker_.CalledOnValidThread().
Backtrace:
	base::debug::StackTrace::StackTrace [0x00007FF7348B63F1+33]
	logging::LogMessage::~LogMessage [0x00007FF73483102C+76]
	base::TestSimpleTaskRunner::PostDelayedTask [0x00007FF733CFB754+112]
	base::win::ObjectWatcher::DoneWaiting [0x00007FF7348A6BD4+148]
	RtlCreateTimer [0x00007FFA2AB2F25D+1165]
	TpSetWait [0x00007FFA2AB316C0+400]
	RtlFindActivationContextSectionString [0x00007FFA2AB1100D+5741]
	BaseThreadInitThunk [0x00007FFA2A850404+20]
	RtlUserThreadStart [0x00007FFA2AB45181+33]

I suspect r407874. Francois: please take a look. Thanks!

These tests are still broken - not just on the FYI builder, but on every single win10 trybot run

https://build.chromium.org/p/chromium.fyi/builders/Win%2010%20Fast%20Ring/builds/2325/steps/unit_tests

https://build.chromium.org/p/tryserver.chromium.win/builders/win10_chromium_x64_rel_ng/builds/267/steps/unit_tests%20%28with%20patch%29%20on%20Windows-10-10586

Please can this be given a higher priority.

Reverted the problematic CL https://codereview.chromium.org/2277333002/

A TaskRunner is supposed to be thread-safe https://cs.chromium.org/chromium/src/base/task_runner.h?l=42 but that property isn't respected by the TestSimpleTaskRunner used in ExtensionWelcomeNotificationTest. A DCHECK fails when ObjectWatcher tries to used that TaskRunner from multiple threads.

ExtensionWelcomeNotificationTest.* passed on Win10 https://build.chromium.org/p/chromium.fyi/builders/Win%2010%20Fast%20Ring/builds/2341/steps/unit_tests

Thanks for fixing this.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/980375e38eac6b3669a25a0d5f2a8991f57a4d55

commit 980375e38eac6b3669a25a0d5f2a8991f57a4d55
Author: fdoray <fdoray@chromium.org>
Date: Tue Sep 06 17:47:07 2016

Make TestSimpleTaskRunner thread-safe.

From task_runner.h:
 "Implementations of TaskRunner should be thread-safe in that all
  methods must be safe to call on any thread."

The fact that TestSimpleTaskRunner doesn't respect this contract is
confusing. It led to a CL being reverted because it caused a DCHECK
failure inside TestSimpleTaskRunner.
https://codereview.chromium.org/2277333002/

This CL ensures that this won't happen again by making
TestSimpleTaskRunner thread-safe.

BUG= 632184 
CQ_INCLUDE_TRYBOTS=master.tryserver.blink:linux_precise_blink_rel

Review-Url: https://codereview.chromium.org/2296923003
Cr-Commit-Position: refs/heads/master@{#416654}

[modify] https://crrev.com/980375e38eac6b3669a25a0d5f2a8991f57a4d55/base/test/test_simple_task_runner.cc
[modify] https://crrev.com/980375e38eac6b3669a25a0d5f2a8991f57a4d55/base/test/test_simple_task_runner.h
[modify] https://crrev.com/980375e38eac6b3669a25a0d5f2a8991f57a4d55/cc/test/ordered_simple_task_runner.h
[modify] https://crrev.com/980375e38eac6b3669a25a0d5f2a8991f57a4d55/chrome/browser/chromeos/policy/heartbeat_scheduler_unittest.cc
[modify] https://crrev.com/980375e38eac6b3669a25a0d5f2a8991f57a4d55/chrome/browser/chromeos/policy/status_uploader_unittest.cc
[modify] https://crrev.com/980375e38eac6b3669a25a0d5f2a8991f57a4d55/chrome/browser/chromeos/policy/system_log_uploader_unittest.cc
[modify] https://crrev.com/980375e38eac6b3669a25a0d5f2a8991f57a4d55/components/policy/core/common/cloud/cloud_policy_refresh_scheduler_unittest.cc
[modify] https://crrev.com/980375e38eac6b3669a25a0d5f2a8991f57a4d55/components/policy/core/common/cloud/external_policy_data_updater_unittest.cc
[modify] https://crrev.com/980375e38eac6b3669a25a0d5f2a8991f57a4d55/components/policy/core/common/policy_statistics_collector_unittest.cc
[modify] https://crrev.com/980375e38eac6b3669a25a0d5f2a8991f57a4d55/device/bluetooth/bluetooth_adapter_win_unittest.cc
[modify] https://crrev.com/980375e38eac6b3669a25a0d5f2a8991f57a4d55/device/bluetooth/bluetooth_task_manager_win_unittest.cc