STR:

1. ./mach run https://samuknet.github.io/test_cases/iframeCSSRotate/ --debug
2. b rust_panic
3. run
4. then wait 30s, then press escape
5. in the terminal:

ERROR:servo: called `Result::unwrap()` on an `Err` value: Error { repr: Custom(Custom { kind: NotFound, error: StringError("Bogus destination port.") }) }

with no backtrace, and the breakpoint doesn't get hit before servo exits.