repro: sign in to an existing account with a Tether host. Chrome will immediately crash when Tether tries to do a host scan.

This is the last few lines of /home/chronos/user/log/chrome before the crash:

[17224:17224:0625/174909.324763:INFO:tether_service.cc(202)] Starting up TetherComponent.
[17224:17224:0625/174909.324906:INFO:host_scanner_impl.cc(101)] Starting Tether host scan. 2 potential host(s) included in the search.

GDB stack trace:

mojo::internal::Serializer<chromeos::device_sync::mojom::RemoteDeviceDataView, cryptauth::RemoteDevice const>::Serialize(cryptauth::RemoteDevice const&, mojo::internal::Buffer*, chromeos::device_sync::mojom::internal::RemoteDevice_Data::BufferWriter*, mojo::internal::SerializationContext*) ()
    at /usr/local/google/home/hansberry/chromium/.cros_cache/chrome-sdk/tarballs/eve+10779.0.0+target_toolchain/usr/bin/../include/c++/v1/string:1226
#0  mojo::internal::Serializer<chromeos::device_sync::mojom::RemoteDeviceDataView, cryptauth::RemoteDevice const>::Serialize(cryptauth::RemoteDevice const&, mojo::internal::Buffer*, chromeos::device_sync::mojom::internal::RemoteDevice_Data::BufferWriter*, mojo::internal::SerializationContext*) ()
    at /usr/local/google/home/hansberry/chromium/.cros_cache/chrome-sdk/tarballs/eve+10779.0.0+target_toolchain/usr/bin/../include/c++/v1/string:1226
#1  0x00005a6ab9dfe8cd in chromeos::secure_channel::mojom::SecureChannelProxy::ListenForConnectionFromDevice(cryptauth::RemoteDevice const&, cryptauth::RemoteDevice const&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, chromeos::secure_channel::ConnectionPriority, mojo::InterfacePtr<chromeos::secure_channel::mojom::ConnectionDelegate>) ()
    at ../../mojo/public/cpp/bindings/lib/serialization_forward.h:42
warning: (Internal error: pc 0x5a6ab9dfe8cc in read in CU, but not in symtab.)
warning: Could not find DWO CU obj/chromeos/services/secure_channel/public/cpp/client/client/secure_channel_client_impl.dwo(0x403c1f87d183be80) referenced by CU at offset 0x3fee9 [in module /opt/google/chrome/chrome]
#2  0x00005a6ab9dfc8e7 in chromeos::secure_channel::SecureChannelClientImpl::PerformListenForConnectionFromDevice(cryptauth::RemoteDeviceRef, cryptauth::RemoteDeviceRef, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, chromeos::secure_channel::ConnectionPriority, mojo::InterfacePtr<chromeos::secure_channel::mojom::ConnectionDelegate>) ()
    at ../../chromeos/services/secure_channel/public/cpp/client/secure_channel_client_impl.cc:116
#3  0x00005a6ab9dfcbc5 in void base::internal::FunctorTraits<void (chromeos::secure_channel::SecureChannelClientImpl::*)(cryptauth::RemoteDeviceRef, cryptauth::RemoteDeviceRef, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, chromeos::secure_channel::ConnectionPriority, mojo::InterfacePtr<chromeos::secure_channel::mojom::ConnectionDelegate>), void>::Invoke<void (chromeos::secure_channel::SecureChannelClientImpl::*)(cryptauth::RemoteDeviceRef, cryptauth::RemoteDeviceRef, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, chromeos::secure_channel::ConnectionPriority, mojo::InterfacePtr<chromeos::secure_channel::mojom::ConnectionDelegate>), base::WeakPtr<chromeos::secure_channel::SecureChannelClientImpl>, cryptauth::RemoteDeviceRef, cryptauth::RemoteDeviceRef, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, chromeos::secure_channel::ConnectionPriority, mojo::InterfacePtr<chromeos::secure_channel::mojom::ConnectionDelegate> >(void (chromeos::secure_channel::SecureChannelClientImpl::*)(cryptauth::RemoteDeviceRef, cryptauth::RemoteDeviceRef, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, chromeos::secure_channel::ConnectionPriority, mojo::InterfacePtr<chromeos::secure_channel::mojom::ConnectionDelegate>), base::WeakPtr<chromeos::secure_channel::SecureChannelClientImpl>&&, cryptauth::RemoteDeviceRef&&, cryptauth::RemoteDeviceRef&&, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >&&, chromeos::secure_channel::ConnectionPriority&&, mojo::InterfacePtr<chromeos::secure_channel::mojom::ConnectionDelegate>&&) () at ../../base/bind_internal.h:507
#4  0x00005a6ab9dfcaea in base::internal::Invoker<base::internal::BindState<void (chromeos::secure_channel::SecureChannelClientImpl::*)(cryptauth::RemoteDeviceRef, cryptauth::RemoteDeviceRef, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> > const&, chromeos::secure_channel::ConnectionPriority, mojo::InterfacePtr<chromeos::secure_channel::mojom::ConnectionDelegate>), base::WeakPtr<chromeos::secure_channel::SecureChannelClientImpl>, cryptauth::RemoteDeviceRef, cryptauth::RemoteDeviceRef, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >, chromeos::secure_channel::ConnectionPriority, mojo::InterfacePtr<chromeos::secure_channel::mojom::ConnectionDelegate> >, void ()>::RunOnce(base::internal::BindStateBase*) () at ../../base/bind_internal.h:627
#5  0x00005a6abaf64d29 in base::debug::TaskAnnotator::RunTask(char const*, base::PendingTask*) () at ../../base/callback.h:99
#6  0x00005a6abaf7ac97 in base::MessageLoop::RunTask(base::PendingTask*) () at ../../base/message_loop/message_loop.cc:319
#7  0x00005a6abaf7b187 in base::MessageLoop::DoWork() () at ../../base/message_loop/message_loop.cc:329
#8  0x00005a6abaff43c9 in base::MessagePumpLibevent::Run(base::MessagePump::Delegate*) () at ../../base/message_loop/message_pump_libevent.cc:210

I initially suspected this was due to DeviceSyncClient not having devices synced yet, but that doesn't seem to be the issue because the logs say "2 potential host(s) included in the search". I'll keep investigating.