If, on Fuchsia, I run these two tests:

out/fuch/bin/run_content_unittests --gtest_filter=VideoCaptureImplTest.EndedBeforeStop:PresentationDispatcherTest.TestStartPresentation

PresentationDispatcherTest CHECKs because there's already a TaskScheduler instance set.

VideoCaptureImplTest causes it to be set by below, but doesn't cause it to be cleared on test shutdown.

[00001.618] 03414.03441> [3:1937305221:0825/174943.400442:1617998:ERROR:task_scheduler.cc(75)] TaskScheduler::SetInstance, 0x794f7fd50700
#00: base::debug::StackTrace::StackTrace(unsigned long) at base/debug/stack_trace_fuchsia.cc:173
#01: base::debug::StackTrace::StackTrace() at base/debug/stack_trace.cc:199
#02: base::TaskScheduler::SetInstance(std::__1::unique_ptr<base::TaskScheduler, std::__1::default_delete<base::TaskScheduler> >) at base/task_scheduler/task_scheduler.cc:76
#03: base::TaskScheduler::Create(base::BasicStringPiece<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >) at base/task_scheduler/task_scheduler.cc:70
#04: base::TaskScheduler::CreateAndStartWithDefaultParams(base::BasicStringPiece<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > >) at base/task_scheduler/task_scheduler.cc:60
#05: content::ChildProcess::ChildProcess(base::ThreadPriority, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, std::__1::unique_ptr<base::TaskScheduler::InitParams, std::__1::default_delete<base::TaskScheduler::InitParams> >) at content/child/child_process.cc:53
#06: content::VideoCaptureImplTest::VideoCaptureImplTest() at content/renderer/media/video_capture_impl_unittest.cc:98
#07: content::VideoCaptureImplTest_EndedBeforeStop_Test::VideoCaptureImplTest_EndedBeforeStop_Test() at content/renderer/media/video_capture_impl_unittest.cc:344
#08: testing::internal::TestFactoryImpl<content::VideoCaptureImplTest_EndedBeforeStop_Test>::CreateTest() at third_party/googletest/src/googletest/include/gtest/internal/gtest-internal.h:484
#09: testing::Test* testing::internal::HandleSehExceptionsInMethodIfSupported<testing::internal::TestFactoryBase, testing::Test*>(testing::internal::TestFactoryBase*, testing::Test* (testing::internal::TestFactoryBase::*)(), char const*) at third_party/googletest/src/googletest/src/gtest.cc:2399
#10: testing::Test* testing::internal::HandleExceptionsInMethodIfSupported<testing::internal::TestFactoryBase, testing::Test*>(testing::internal::TestFactoryBase*, testing::Test* (testing::internal::TestFactoryBase::*)(), char const*) at third_party/googletest/src/googletest/src/gtest.cc:2452
#11: testing::TestInfo::Run() at third_party/googletest/src/googletest/src/gtest.cc:2644
#12: testing::TestCase::Run() at third_party/googletest/src/googletest/src/gtest.cc:2770
#13: testing::internal::UnitTestImpl::RunAllTests() at third_party/googletest/src/googletest/src/gtest.cc:4647
#14: bool testing::internal::HandleSehExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) at third_party/googletest/src/googletest/src/gtest.cc:2399
#15: bool testing::internal::HandleExceptionsInMethodIfSupported<testing::internal::UnitTestImpl, bool>(testing::internal::UnitTestImpl*, bool (testing::internal::UnitTestImpl::*)(), char const*) at third_party/googletest/src/googletest/src/gtest.cc:2452
#16: testing::UnitTest::Run() at third_party/googletest/src/googletest/src/gtest.cc:4256
#17: RUN_ALL_TESTS() at third_party/googletest/src/googletest/include/gtest/gtest.h:2237
#18: base::TestSuite::Run() at base/test/test_suite.cc:270
#19: content::UnitTestTestSuite::Run() at content/public/test/unittest_test_suite.cc:45
#20: int base::internal::FunctorTraits<int (content::UnitTestTestSuite::*)(), void>::Invoke<content::UnitTestTestSuite*>(int (content::UnitTestTestSuite::*)(), content::UnitTestTestSuite*&&) at base/bind_internal.h:194
#21: int base::internal::InvokeHelper<false, int>::MakeItSo<int (content::UnitTestTestSuite::* const&)(), content::UnitTestTestSuite*>(int (content::UnitTestTestSuite::* const&)(), content::UnitTestTestSuite*&&) at base/bind_internal.h:263
#22: int base::internal::Invoker<base::internal::BindState<int (content::UnitTestTestSuite::*)(), base::internal::UnretainedWrapper<content::UnitTestTestSuite> >, int ()>::RunImpl<int (content::UnitTestTestSuite::* const&)(), std::__1::tuple<base::internal::UnretainedWrapper<content::UnitTestTestSuite> > const&, 0ul>(int (content::UnitTestTestSuite::* const&)(), std::__1::tuple<base::internal::UnretainedWrapper<content::UnitTestTestSuite> > const&, std::__1::integer_sequence<unsigned long, 0ul>) at base/bind_internal.h:335
#23: base::internal::Invoker<base::internal::BindState<int (content::UnitTestTestSuite::*)(), base::internal::UnretainedWrapper<content::UnitTestTestSuite> >, int ()>::Run(base::internal::BindStateBase*) at base/bind_internal.h:317
#24: base::Callback<int (), (base::internal::CopyMode)1, (base::internal::RepeatMode)1>::Run() const & at base/callback.h:80
#25: base::(anonymous namespace)::LaunchUnitTestsInternal(base::Callback<int (), (base::internal::CopyMode)1, (base::internal::RepeatMode)1> const&, unsigned long, int, bool, base::Callback<void (), (base::internal::CopyMode)1, (base::internal::RepeatMode)1> const&) at base/test/launcher/unit_test_launcher.cc:216
#26: base::LaunchUnitTests(int, char**, base::Callback<int (), (base::internal::CopyMode)1, (base::internal::RepeatMode)1> const&) at base/test/launcher/unit_test_launcher.cc:475
#27: main at content/test/run_all_unittests.cc:20
#28: pc 0x66fa2961a04e (libc.so,0x1c04e)