This test flakes more than 50% of the time on MacOS:
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=TabManagerTest.TabPendingFreezeAndUnfreeze

It also crashes on linux.

The crash is:
[15125:775:0620/133040.346643:FATAL:tab_lifecycle_unit.cc(792)] Check failed: false.
0 base::debug::StackTrace::StackTrace(unsigned long) + 28
1 logging::LogMessage::~LogMessage() + 223
2 resource_coordinator::TabLifecycleUnitSource::TabLifecycleUnit::OnLifecycleUnitStat
3 resource_coordinator::LifecycleUnitBase::SetState(mojom::LifecycleUnitState, mojom:
4 non-virtual thunk to resource_coordinator::TabLifecycleUnitSource::OnLifecycleState
5 void resource_coordinator::PageSignalReceiver::NotifyObserversIfKnownCu<void (resou
6 resource_coordinator::mojom::PageSignalReceiverStubDispatch::Accept(resource_coordi
7 mojo::InterfaceEndpointClient::HandleValidatedMessage(mojo::Message*) + 982


This looks related to a recent patch:
RC: Add LifecycleUnit::Unfreeze().
https://chromium-review.googlesource.com/c/chromium/src/+/1099973

fdoray, can you please take a look?