Assining to ramyasharma because this CL is the suspected culprit:

https://codereview.chromium.org/2623033006

I've created a speculative revert here: https://codereview.chromium.org/2660333004/

FindIt results link: https://findit-for-me.appspot.com/waterfall/build-failure?url=https://build.chromium.org/p/chromium.win/builders/Win7%20Tests%20%28dbg%29%281%29/builds/56932

Test output: [ RUN      ] MTPDeviceDelegateImplWinTest.GalleryNameMTP
[5188:6024:0129/215605.045:40831452:FATAL:media_file_system_registry.cc(765)] Check failed: StorageMonitor::GetInstance().
Backtrace:
	base::debug::StackTrace::StackTrace [0x0C065067+55]
	base::debug::StackTrace::StackTrace [0x0C064CA1+17]
	logging::LogMessage::~LogMessage [0x0C0B321B+59]
	MediaFileSystemRegistry::~MediaFileSystemRegistry [0x0464D53B+139]
	MediaFileSystemRegistry::`scalar deleting destructor' [0x04650C3F+15]
	std::default_delete<MediaFileSystemRegistry>::operator() [0x03B18ACA+42]
	std::unique_ptr<MediaFileSystemRegistry,std::default_delete<MediaFileSystemRegistry> >::~unique_ptr<MediaFileSystemRegistry,std::default_delete<MediaFileSystemRegistry> > [0x03B1830B+43]
	TestingBrowserProcess::~TestingBrowserProcess [0x03B18596+374]
	TestingBrowserProcess::`scalar deleting destructor' [0x03B18C7F+15]
	TestingBrowserProcess::DeleteInstance [0x03B18E38+56]
	testing::EmptyTestEventListener::OnTestCaseStart [0x03B24EC9+201]
	testing::internal::TestEventRepeater::OnTestEnd [0x03D2433B+91]
	testing::TestInfo::Run [0x03D27F54+260]
	testing::TestCase::Run [0x03D27D9F+191]
	testing::internal::UnitTestImpl::RunAllTests [0x03D28385+661]
	testing::internal::HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl,bool> [0x03D0F824+52]
	testing::UnitTest::Run [0x03D2807F+207]
	RUN_ALL_TESTS [0x03B4008F+15]
	base::TestSuite::Run [0x03B401C3+115]
	content::UnitTestTestSuite::Run [0x07FBBD46+22]
	??$Invoke@PAVUnitTestTestSuite@content@@$$V@?$FunctorTraits@P8UnitTestTestSuite@content@@AEHXZX@internal@base@@SAHP8UnitTestTestSuite@content@@AEHXZ$$QAPAV34@@Z [0x07FA92D2+18]
	base::internal::InvokeHelper<0,int>::MakeItSo<int (__thiscall content::UnitTestTestSuite::*const &)(void),content::UnitTestTestSuite *> [0x07FA9334+36]
	base::internal::Invoker<base::internal::BindState<int (__thiscall content::UnitTestTestSuite::*)(void),base::internal::UnretainedWrapper<content::UnitTestTestSuite> >,int __cdecl(void)>::RunImpl<int (__thiscall content::UnitTestTestSuite::*const &)(void), [0x07FA938B+59]
	base::internal::Invoker<base::internal::BindState<int (__thiscall content::UnitTestTestSuite::*)(void),base::internal::UnretainedWrapper<content::UnitTestTestSuite> >,int __cdecl(void)>::Run [0x07FA9554+36]
	base::internal::RunMixin<base::Callback<int __cdecl(void),1,1> >::Run [0x02BDF97F+63]
	base::LaunchUnitTests [0x03B49E7B+411]
	base::LaunchUnitTests [0x03B49CB1+81]
	main [0x07FA9689+233]
	invoke_main [0x07FA772E+30] (f:\ddctools\crtcstartup\src\startup\exe_common.inl:64)
	__scrt_common_main_seh [0x07FA75B0+336] (f:\ddctools\crtcstartup\src\startup\exe_common.inl:253)
	__scrt_common_main [0x07FA744D+13] (f:\ddctools\crtcstartup\src\startup\exe_common.inl:296)
	mainCRTStartup [0x07FA7748+8] (f:\ddctools\crtcstartup\src\startup\exe_main.cpp:17)
	BaseThreadInitThunk [0x759D336A+18]
	RtlInitializeExceptionChain [0x779292B2+99]
	RtlInitializeExceptionChain [0x77929285+54]

The bot is now fixed, so removing this issue from the sheriff queue.

The changes made in my CL seem completely unrelated to the breakage here. The only common link seems is using TestingBrowserProcess in the test that failed - chrome/browser/media_galleries/media_file_system_registry_unittest.cc, and my test chrome/browser/external_protocol/external_protocol_handler_unittest.cc.

fdoray@ introduced the TestingBrowserProcess in https://codereview.chromium.org/2654303002, that introduced a DCHECK in MediaFileSystemRegistry::~MediaFileSystemRegistry(), that is failing with my changes. Maybe some kind of race condition when resetting / deleting the browser process is causing this? Or my changes exposed an issue with the change https://codereview.chromium.org/2654303002.

fdoray@ Could you please take a look at what could cause your test to fail, from my CL?

ramyasharma@: Can you see if your CL still causes a unit_tests failure after this fix https://codereview.chromium.org/2664073003/?

Looks like this test still isn't happy after the change in #5. See: https://luci-milo.appspot.com/buildbot/chromium.win/Win7%20Tests%20%281%29/63111.

Reverting now.

fdoray: looks like there's something more complex going on here with destruction orders in the media gallery test. Do you have any theories?

For instance, is the fact that the failing test uses ChromeRenderViewHostTestHarness versus the non-failing test using testing::Test (and its own thread bundle) an issue?

Hi fdoray@, any update on this? My cl is blocked on this issue. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a80d18c3fa89a2cc0b7c01a22a6aa1df796f550d

commit a80d18c3fa89a2cc0b7c01a22a6aa1df796f550d
Author: mahmadi <mahmadi@chromium.org>
Date: Fri Feb 03 17:05:12 2017

Disables MTPDeviceDelegateImplWinTest.GalleryNameMTP

BUG= 686803 

TBR=reillyg@

Review-Url: https://codereview.chromium.org/2675963003
Cr-Commit-Position: refs/heads/master@{#448013}

[modify] https://crrev.com/a80d18c3fa89a2cc0b7c01a22a6aa1df796f550d/chrome/browser/media_galleries/win/mtp_device_delegate_impl_win_unittest.cc

 Issue 688472  has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/99827662a4a6c77083b111a98b6e32797f9b5654

commit 99827662a4a6c77083b111a98b6e32797f9b5654
Author: fdoray <fdoray@chromium.org>
Date: Mon Feb 06 22:00:32 2017

Fix and enable MTPDeviceDelegateImplWinTest.GalleryNameMTP.

TestStorageMonitor must be destroyed after MediaFileSystemRegistry
because MediaFileSystemRegistry uses it in its destructor.

BUG= 686803 

Review-Url: https://codereview.chromium.org/2677943003
Cr-Commit-Position: refs/heads/master@{#448405}

[modify] https://crrev.com/99827662a4a6c77083b111a98b6e32797f9b5654/chrome/browser/media_galleries/win/mtp_device_delegate_impl_win_unittest.cc