Example logs:
https://ci.chromium.org/buildbot/chromium.fyi/Mojo%20Linux/14027
https://ci.chromium.org/buildbot/chromium.fyi/Mojo%20Linux/14028

Log:
crash log for renderer (pid <unknown>):
STDOUT: <empty>
STDERR: CONSOLE ERROR: line 23: Only fetch keepalive is allowed during onfreeze: http://web-platform.test:8001/lifecycle/resources/foo.txt
STDERR: CONSOLE ERROR: line 42: Only fetch keepalive is allowed during onfreeze: http://web-platform.test:8001/lifecycle/resources/foo.txt
STDERR: CONSOLE WARNING: line 40: Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check https://xhr.spec.whatwg.org/.
STDERR: CONSOLE ERROR: line 42: Only fetch keepalive is allowed during onfreeze: http://web-platform.test:8001/lifecycle/resources/foo.txt
STDERR: [1:1:0531/133558.285693:FATAL:frame_scheduler_impl.cc(599)] Check failed: !parent_page_scheduler_->IsPageVisible(). 
STDERR: #0 0x00000380a3fc base::debug::StackTrace::StackTrace()
STDERR: #1 0x000003785a9b logging::LogMessage::~LogMessage()
STDERR: #2 0x000002cf2a30 blink::scheduler::FrameSchedulerImpl::CalculateThrottlingState()
STDERR: #3 0x000002ce7290 blink::FrameOrWorkerScheduler::NotifyThrottlingObservers()
STDERR: #4 0x000002d0d519 blink::scheduler::PageSchedulerImpl::SetPageFrozenImpl()
STDERR: #5 0x000006b4ca1f gin::internal::Dispatcher<>::DispatchToCallback()
STDERR: #6 0x0000022a6753 v8::internal::FunctionCallbackArguments::Call()
STDERR: #7 0x0000022a4ab2 v8::internal::(anonymous namespace)::HandleApiCallHelper<>()
STDERR: #8 0x0000022a2e78 v8::internal::Builtin_Impl_HandleApiCall()
STDERR: #9 0x0000022a28bd v8::internal::Builtin_HandleApiCall()
STDERR: #10 0x1f4aac6b3c24 <unknown>
STDERR: