This VM is failing webkit_layout_tests all the time:
https://chromium-swarm.appspot.com/bot?id=vm143-m4&sort_stats=total%3Adesc

Please see this tryjob for example:
https://ci.chromium.org/p/chromium/builders/luci.chromium.try/win7_chromium_rel_ng/27572

and this shard:
https://chromium-swarm.appspot.com/task?id=3e61e4c7c0afa010&refresh=10&show_raw=1

I just clicked the "Shutdown gracefully" button in the Swarming UI, so this is only P2. Here's the log excerpt. May need to be reimaged.

18:15:23.608 3376 Checking system dependencies ...
18:15:24.107 3376 "e:\b\swarm_slave\w\ir\out\Release\content_shell.exe --check-layout-test-sys-deps" took 0.50s
18:15:24.107 3376 System dependencies check failed.
18:15:24.107 3376 To override, invoke with --nocheck-sys-deps
18:15:24.107 3376 
18:15:24.107 3376 
DevTools listening on ws://127.0.0.1:52775/devtools/browser/66a3e2a8-f617-4589-bab0-b6830cf40bbc
[5576:9248:0628/181523.842:ERROR:gpu_process_host.cc(586)] BrowserMainRunner::ExitedMainMessageLoop()
[5576:9248:0628/181523.857:WARNING:discardable_shared_memory_manager.cc(431)] Some MojoDiscardableSharedMemoryManagerImpls are still alive. They will be leaked.
[5576:8500:0628/181523.873:WARNING:scoped_temp_dir.cc(23)] Could not delete temp dir in dtor.
[5576:4468:0628/181523.873:FATAL:at_exit.cc(63)] Check failed: !g_top_manager->processing_callbacks_. 
Backtrace:
	base::debug::StackTrace::StackTrace [0x028B05B0+32]
	base::debug::StackTrace::StackTrace [0x028AFD6D+13]
	logging::LogMessage::~LogMessage [0x028C8523+83]
	base::AtExitManager::RegisterTask [0x028A970A+122]
	base::AtExitManager::RegisterCallback [0x028A9678+184]
	base::internal::CompleteLazyInstance [0x028C7AEF+31]
	disk_cache::File::Init [0x03C7198F+491]
	disk_cache::File::Init [0x03C7186D+201]
	disk_cache::MappedFile::Init [0x03C7243E+102]
	disk_cache::BlockFiles::OpenBlockFile [0x03C6AEB4+202]
	disk_cache::BlockFiles::Init [0x03C6AC50+164]
	disk_cache::BackendImpl::SyncInit [0x031961A6+430]
	disk_cache::BackendIO::ExecuteBackendOperation [0x03C68D96+58]
	base::debug::TaskAnnotator::RunTask [0x028B0DD2+306]
	base::internal::IncomingTaskQueue::RunTask [0x030D9EAC+108]
	base::MessageLoop::RunTask [0x028D1637+519]
	base::MessageLoop::DeferOrRunPendingTask [0x028D198D+157]
	base::MessageLoop::DoWork [0x028D1BBA+506]
	base::MessagePumpForIO::DoRunLoop [0x028D3E35+133]
	base::MessagePumpWin::Run [0x028D316E+110]
	base::MessageLoop::Run [0x028D1154+116]
	base::RunLoop::Run [0x028EC9FC+204]
	base::Thread::Run [0x02903224+164]
	base::Thread::ThreadMain [0x029034AD+621]
	base::PlatformThread::SetCurrentThreadPriority [0x02901675+533]
	BaseThreadInitThunk [0x7596338A+18]
	RtlInitializeExceptionChain [0x76F69F72+99]
	RtlInitializeExceptionChain [0x76F69F45+54]

18:15:24.107 3376 
18:15:24.107 3376 For complete build requirements, please see:
18:15:24.122 3376 https://chromium.googlesource.com/chromium/src/+/master/docs/windows_build_instructions.md
18:15:24.122 3376 
18:15:24.122 3376 Testing completed. Exit status: 252