I built the mus_demo, and launched it via mojo_runner:

./out/asan/mojo_runner mojo:mus_demo

However upon closing the mus_demo window the mojo_runner process is still running. You have to manually kill it.

GN args:
target_os = "chromeos"                                                          
is_debug = true                                                                 
use_goma = true                                                                 
is_component_build = false                                                      
enable_nacl = true