Crash stack below. It seems that some browsertests pass in single-process mode, others crash with same stacktrace.

$ cr run headless_shell --single-process
ninja: Entering directory `/usr/local/google/code/clankium_headless_roll/src/out/Release'
[1/1] LINK ./headless_shell
[0221/084204.944325:WARNING:histograms.cc(40)] Started multiple compositor clients (Browser, Renderer) in one process. Some metrics will be disabled.
Received signal 11 SEGV_MAPERR 144300000024
#0 0x7f893daf0267 base::debug::StackTrace::StackTrace()
#1 0x7f893daefddf base::debug::(anonymous namespace)::StackDumpSignalHandler()
#2 0x7f893d812330 <unknown>
#3 0x7f893db51c2a std::_Rb_tree<>::_M_insert_unique_<>()
#4 0x7f893db51805 base::SupportsUserData::SetUserData()
#5 0x7f893ca37266 content::(anonymous namespace)::GetSiteProcessMapForBrowserContext()
#6 0x7f893ca2e4c2 content::RenderProcessHostImpl::UnregisterHost()
#7 0x7f893ca2ddde content::RenderProcessHostImpl::~RenderProcessHostImpl()
#8 0x7f893ca2e559 content::RenderProcessHostImpl::~RenderProcessHostImpl()
#9 0x7f893ca2dbdc content::RenderProcessHostImpl::ShutDownInProcessRenderer()
#10 0x7f893c7f7ed7 content::BrowserMainLoop::ShutdownThreadsAndCleanUp()
#11 0x7f893c7fb79c content::BrowserMainRunnerImpl::Shutdown()
#12 0x0000004b8505 headless::HeadlessContentMainDelegate::RunProcess()
#13 0x7f893cde8abc content::RunNamedProcessTypeMain()
#14 0x7f893cde928c content::ContentMainRunnerImpl::Run()
#15 0x7f893cde7e40 content::ContentMain()
#16 0x0000004b2cc3 headless::(anonymous namespace)::RunContentMain()
#17 0x0000004b2d3a headless::HeadlessBrowserMain()
#18 0x0000004891e5 headless::HeadlessShellMain()
#19 0x7f893a8e3f45 __libc_start_main
#20 0x00000047e4a9 <unknown>
  r8: 00007ffcce818500  r9: 000000006c696843 r10: 000000000080736e r11: 00007f893aa48390
 r12: 00007ffcce8184a8 r13: 0000144386aeba18 r14: 000014438591d0c0 r15: 0000144300000004
  di: 000014438591d0c0  si: 000014438591d0c8  bp: 0000144386ade270  bx: 000014438591d0c8
  dx: 00007ffcce8184a8  ax: 000014438591d0c8  cx: 0000144386aeba00  sp: 00007ffcce818460
  ip: 00007f893db51c2a efl: 0000000000010202 cgf: 0000000000000033 erf: 0000000000000004
 trp: 000000000000000e msk: 0000000000000000 cr2: 0000144300000024


irisu@ experienced a different crash:

$ cr run headless_browsertests --gtest_filter=HeadlessWebContentsTest.Focus --single-process
There's a fatal error: 
[138922:138922:0221/144911.147681:445215356239:FATAL:lock_impl_posix.cc(65)]
Check failed: rv == 0 (22 vs. 0). Invalid argument