Chrome ToT r460396 on linux desktop with target_os=chromeos.

* Run --mash
* Click system tray > Sign out

This causes the ash process to exit which causes the root service manager process to exit.

[5365:5379:0329/151108.771005:26487399246:FATAL:interface_endpoint_client.cc(166)] Check failed: thread_checker_.CalledOnValidThread(). 
#0 0x7f41ddf7cf17 base::debug::StackTrace::StackTrace()
#1 0x7f41ddf9ed9a logging::LogMessage::~LogMessage()
#2 0x7f41de4e746a mojo::InterfaceEndpointClient::~InterfaceEndpointClient()
#3 0x7f41de4e7579 mojo::InterfaceEndpointClient::~InterfaceEndpointClient()
#4 0x7f41de4e123e mojo::internal::BindingStateBase::Close()
#5 0x55e6cee10689 std::_Rb_tree<>::_M_erase()
#6 0x55e6cef2a165 ui::GpuService::~GpuService()
#7 0x55e6cef2a489 ui::GpuService::~GpuService()
#8 0x55e6cef27d7e ui::GpuMain::TearDownOnGpuThread()
#9 0x7f41ddf7dba3 _ZNO4base8CallbackIFvvELNS_8internal8CopyModeE0ELNS2_10RepeatModeE0EE3RunEv
#10 0x7f41ddf7d9da base::debug::TaskAnnotator::RunTask()
#11 0x7f41ddfababd base::MessageLoop::RunTask()
#12 0x7f41ddfabd58 base::MessageLoop::DeferOrRunPendingTask()
#13 0x7f41ddfac156 base::MessageLoop::DoWork()
#14 0x7f41ddfae889 base::MessagePumpLibevent::Run()
#15 0x7f41ddfab83a base::MessageLoop::RunHandler()
#16 0x7f41ddfde51f base::RunLoop::Run()
#17 0x7f41de01ba7b base::Thread::Run()
#18 0x7f41de01bf3e base::Thread::ThreadMain()
#19 0x7f41de013c2c base::(anonymous namespace)::ThreadFunc()
#20 0x7f41de0f6184 start_thread
#21 0x7f41d4ee2bed clone

Shutdown/sign out isn't fully hooked up yet. However, this used to exit cleanly (~last week).

I'm concerned that this will cause shutdown crashes in my MashLogin autotest, though I have not verified that.

Sadrul, can you find an owner?