Origin::Nonce has a mutable field that is written to when being copied (and in other cases). This means that calling two const methods on an Origin object from two different threads may race. The expectation in C++11 is that const methods do not race with each other (see for example Herb Sutters blog https://herbsutter.com/2013/05/24/gotw-6a-const-correctness-part-1-3/).

+dcheng from the OWNERS file, I have no idea what component this would be.