Hi, seems https://codereview.chromium.org/2329543002 is causing a lot of mus_ws_unittests to fail:

https://build.chromium.org/p/chromium.linux/builders/Linux%20Tests%20%28dbg%29%281%29%2832%29/builds/33286

relevant parts:
[32650:32650:0912/155014:4585063712:ERROR:window_tree.cc(1331)] Not implemented reached in virtual void ui::ws::WindowTree::OnWindowInputEventAck(uint32_t, mojom::EventResult): Wrong event acked. event_id=0, event_ack_id_=24847302
Received signal 11 SEGV_MAPERR 000000000004
#0 0x0000f73092a4 base::debug::StackTrace::StackTrace()
#1 0x0000f7308dcb base::debug::(anonymous namespace)::StackDumpSignalHandler()
#2 0x0000f76e4420 ([vdso]+0x41f)
#3 0x0000f74da03f base::Thread::Stop()
#4 0x00000836757f ui::GpuMain::~GpuMain()
#5 0x00000859bc5f ui::ws::GpuServiceProxy::~GpuServiceProxy()
#6 0x00000859bda3 ui::ws::GpuServiceProxy::~GpuServiceProxy()
#7 0x0000080e46a9 std::default_delete<>::operator()()
#8 0x00000857552d std::unique_ptr<>::reset()
#9 0x000008571d69 std::unique_ptr<>::~unique_ptr()
#10 0x00000856b374 ui::ws::WindowServer::~WindowServer()
#11 0x00000856bca3 ui::ws::WindowServer::~WindowServer()
#12 0x0000080e6ff9 std::default_delete<>::operator()()
#13 0x00000810688d std::unique_ptr<>::reset()
#14 0x000008103987 ui::ws::test::WindowServerTestHelper::~WindowServerTestHelper()
#15 0x000008103c8b ui::ws::test::WindowEventTargetingHelper::~WindowEventTargetingHelper()
#16 0x0000081c03d3 ui::ws::test::WindowTreeTest::~WindowTreeTest()
#17 0x0000081c021b ui::ws::test::WindowTreeTest_EventAck_Test::~WindowTreeTest_EventAck_Test()
#18 0x0000081c0263 ui::ws::test::WindowTreeTest_EventAck_Test::~WindowTreeTest_EventAck_Test()
#19 0x000008377092 base::RefCountedThreadSafe<>::DeleteInternal()
#20 0x000008670b90 testing::internal::HandleSehExceptionsInMethodIfSupported<>()
#21 0x000008663c03 testing::internal::HandleExceptionsInMethodIfSupported<>()
#22 0x0000086565a0 testing::TestInfo::Run()
#23 0x000008656d00 testing::TestCase::Run()
#24 0x00000865e65f testing::internal::UnitTestImpl::RunAllTests()
#25 0x000008673190 testing::internal::HandleSehExceptionsInMethodIfSupported<>()
#26 0x000008665973 testing::internal::HandleExceptionsInMethodIfSupported<>()
#27 0x00000865e268 testing::UnitTest::Run()
#28 0x0000085b6e6d RUN_ALL_TESTS()
#29 0x0000085b5761 base::TestSuite::Run()
#30 0x0000081942ee _ZN4base8internal13FunctorTraitsIMN4mojo17AssociatedBindingIN2ui5mojom13WindowManagerEEEFvvEvE6InvokeIPS7_JEEEvS9_OT_DpOT0_
#31 0x0000081941bb _ZN4base8internal12InvokeHelperILb0EvE8MakeItSoIRKMN4mojo17AssociatedBindingIN2ui5mojom13WindowManagerEEEFvvEJPS9_EEEvOT_DpOT0_
#32 0x0000081c5fce _ZN4base8internal7InvokerINS0_9BindStateIMNS_9TestSuiteEFivEJNS0_17UnretainedWrapperIS3_EEEEEFivEE7RunImplIRKS5_RKSt5tupleIJS7_EEJLj0EEEEiOT_OT0_NS_13IndexSequenceIJXspT1_EEEE
#33 0x0000081c5d71 _ZN4base8internal7InvokerINS0_9BindStateIMNS_9TestSuiteEFivEJNS0_17UnretainedWrapperIS3_EEEEEFivEE3RunEPNS0_13BindStateBaseE
#34 0x00000819447e base::Callback<>::Run()
#35 0x0000085b92b9 base::(anonymous namespace)::LaunchUnitTestsInternal()
#36 0x0000085b90a3 base::LaunchUnitTests()
#37 0x0000081c5bbe MasterProcessMain()
#38 0x0000084f514b main
#39 0x0000f34a7533 __libc_start_main
#40 0x00000808c431 <unknown>
  gs: 00000063  fs: 00000000  es: 0000002b  ds: 0000002b
 edi: 089edae4 esi: 089edd58 ebp: ffdc0d58 esp: ffdc0b60
 ebx: 089f2edc edx: 09258301 ecx: 00000000 eax: 00000000
 trp: 0000000e err: 00000004  ip: f74da03f  cs: 00000023
 efl: 00010202 usp: ffdc0b60  ss: 0000002b
[end of stack trace]