In helping a developer diagnose a bug in which they were not invoking a Mojo callback before it was destroyed I noticed that we could, instead of using InterfaceEndpointClient::RaiseError to close the pipe, call CloseWithReason and provide an error code and message indicating this failure mode. While C++ code does not normally look at these error reasons the JavaScript bindings will reject the Promise with an error containing this reason and this would be useful for debugging.

rockot@, opinions?