Please see https://build.chromium.org/p/chromium.fyi/builders/Mojo%20Linux/builds/5793

Seems likely to be related to: https://chromium-review.googlesource.com/669300

You could run the test with the following flag to enable network service:

content_browsertests --enable-features=NetworkService 


[ RUN      ] DownloadContentTest.FetchErrorResponseBodyResumption
Xlib:  extension "RANDR" missing on display ":99".
DevTools listening on ws://127.0.0.1:39220/devtools/browser/087b5c12-8187-46e2-ba36-104a2176f195
[25676:25696:0928/154703.341355:29990109192:WARNING:child_process_launcher_helper_posix.cc(118)] Ignoring invalid file v8_context_snapshot.bin
[25702:25702:0928/154703.362772:29990130610:ERROR:gpu_info.cc(103)] No active GPU found, returning primary GPU.
[25705:25712:0928/154703.438660:29990206499:ERROR:url_loader_impl.cc(238)] Not implemented reached in virtual void content::URLLoaderImpl::SetPriority(net::RequestPriority, int32_t)
BrowserTestBase received signal: Terminated. Backtrace:
#0 0x00000258b367 base::debug::StackTrace::StackTrace()
#1 0x000002239351 content::(anonymous namespace)::DumpStackTraceSignalHandler()
#2 0x7f0adaec6cb0 <unknown>
#3 0x7f0adaf80c5d __poll
#4 0x7f0aded57fe4 <unknown>
#5 0x7f0aded580ec g_main_context_iteration
#6 0x0000025ade33 base::MessagePumpGlib::Run()
#7 0x0000025ab3fa base::MessageLoop::Run()
#8 0x0000025ce0b6 base::RunLoop::Run()
#9 0x0000022550cc content::RunMessageLoop()
#10 0x00000224290b content::DownloadUpdatedObserver::WaitForEvent()
#11 0x000000537fbb content::DownloadContentTest_FetchErrorResponseBodyResumption_Test::RunTestOnMainThread()
#12 0x0000022390bf content::BrowserTestBase::ProxyRunTestOnMainThreadLoop()
#13 0x0000022a3299 content::ShellBrowserMainParts::PreMainMessageLoopRun()
#14 0x000001bcb7dd content::BrowserMainLoop::PreMainMessageLoopRun()
#15 0x000001ff6ac7 content::StartupTaskRunner::RunAllTasksNow()
#16 0x000001bc993e content::BrowserMainLoop::CreateStartupTasks()
#17 0x000001bce5b3 content::BrowserMainRunnerImpl::Initialize()
#18 0x0000022894ec ShellBrowserMain()
#19 0x00000228066e content::ShellMainDelegate::RunProcess()
#20 0x000001aebec6 content::RunNamedProcessTypeMain()
#21 0x000001aeca37 content::ContentMainRunnerImpl::Run()
#22 0x0000037a6d20 service_manager::Main()
#23 0x000000fbe3a2 content::ContentMain()
#24 0x000002238d49 content::BrowserTestBase::SetUp()
#25 0x00000222f66e content::ContentBrowserTest::SetUp()
#26 0x000000a634de testing::Test::Run()
#27 0x000000a63f50 testing::TestInfo::Run()
#28 0x000000a64437 testing::TestCase::Run()
#29 0x000000a6a927 testing::internal::UnitTestImpl::RunAllTests()
#30 0x000000a6a5b3 testing::UnitTest::Run()
#31 0x000002262008 base::TestSuite::Run()
#32 0x000002233043 content::ContentTestLauncherDelegate::RunTestSuite()
#33 0x000002250045 content::LaunchTests()
#34 0x000002232ff2 main
#35 0x7f0adaeb1f45 __libc_start_main
#36 0x000000486890 <unknown>