On ToT chrome started with --mash, there's a black background and chrome fails to start. This is printed to the console:

[18671:18671:0808/120253:FATAL:software_output_device_mus.cc(43)] Check failed: uploader. 
#0 0x7ff2a85801de base::debug::StackTrace::StackTrace()
#1 0x7ff2a85e782f logging::LogMessage::~LogMessage()
#2 0x7ff2a24e5d35 content::SoftwareOutputDeviceMus::EndPaint()
#3 0x7ff29f8050e3 cc::SoftwareRenderer::FinishDrawingFrame()
#4 0x7ff29f796e28 cc::DirectRenderer::DrawFrame()
#5 0x7ff29bb9a69a cc::Display::DrawAndSwap()
#6 0x7ff29bbaf022 cc::DisplayScheduler::DrawAndSwap()
#7 0x7ff29bbae6e2 cc::DisplayScheduler::AttemptDrawAndSwap()
#8 0x7ff29bbae0dc cc::DisplayScheduler::OnBeginFrameDeadline()

gn args:
enable_nacl = false                                                            
enable_ipc_fuzzer = false                                                      
enable_package_mash_services = true                                            
is_debug = true                                                                
use_goma = true