Since at least https://ci.chromium.org/p/chromium/builders/luci.chromium.ci/Mac10.11%20Tests/27804, Mac 10.11 browsertests have often had the below DCHECK go off. I looked at the commits in that run and the couple runs before but didn't see anything obvious, and also looked through recent rolls of crashpad but again didn't see anything suspicious in the commits being brought in. Mark, any thoughts?

[ RUN      ] ChromeContentBrowserClientBrowserTest.SitePerProcessNavigation
[0702/125406.779347:ERROR:mach_extensions.cc(68)] bootstrap_check_in org.chromium.crashpad.child_port_handshake.7358.115704.YLVEVTGTFTEBUIPO: unknown error code (141)
[0702/125406.779472:FATAL:child_port_handshake.cc(111)] Check failed: server_port.is_valid().
0   crashpad_handler                    0x000000010aa3c6bc base::debug::StackTrace::StackTrace(unsigned long) + 28
1   crashpad_handler                    0x000000010aa299c1 logging::LogMessage::~LogMessage() + 225
2   crashpad_handler                    0x000000010aa46394 crashpad::ChildPortHandshake::RunServerForFD(base::ScopedGeneric<int, base::internal::ScopedFDCloseTraits>, crashpad::ChildPortHandshake::PortRightType) + 516
3   crashpad_handler                    0x000000010aa18876 crashpad::HandlerMain(int, char**, std::__1::vector<std::__1::unique_ptr<crashpad::UserStreamDataSource, std::__1::default_delete<crashpad::UserStreamDataSource> >, std::__1::allocator<std::__1::unique_ptr<crashpad::UserStreamDataSource, std::__1::default_delete<crashpad::UserStreamDataSource> > > > const*) + 4790
4   libdyld.dylib                       0x00007fff989965ad start + 1
5   ???                                 0x0000000000000008 0x0 + 8
[0702/125406.780147:ERROR:file_io.cc(89)] ReadExactly: expected 4, observed 0
[0702/125406.780941:ERROR:mach_extensions.cc(68)] bootstrap_check_in org.chromium.crashpad.child_port_handshake.7356.115675.WLILIGUWIWDITSQJ: unknown error code (141)
[0702/125406.781059:FATAL:child_port_handshake.cc(111)] Check failed: server_port.is_valid().
0   crashpad_handler                    0x000000010aec16bc base::debug::StackTrace::StackTrace(unsigned long) + 28
1   crashpad_handler                    0x000000010aeae9c1 logging::LogMessage::~LogMessage() + 225
2   crashpad_handler                    0x000000010aecb394 crashpad::ChildPortHandshake::RunServerForFD(base::ScopedGeneric<int, base::internal::ScopedFDCloseTraits>, crashpad::ChildPortHandshake::PortRightType) + 516
3   crashpad_handler                    0x000000010ae9d876 crashpad::HandlerMain(int, char**, std::__1::vector<std::__1::unique_ptr<crashpad::UserStreamDataSource, std::__1::default_delete<crashpad::UserStreamDataSource> >, std::__1::allocator<std::__1::unique_ptr<crashpad::UserStreamDataSource, std::__1::default_delete<crashpad::UserStreamDataSource> > > > const*) + 4790
4   libdyld.dylib                       0x00007fff989965ad start + 1