"Linux ci_yaml engine roller"  failing repeatedly on "generate jspb" step

https://ci.chromium.org/p/flutter/builders/prod/Linux%20ci_yaml%20engine%20roller

For example

https://ci.chromium.org/ui/p/flutter/builders/prod/Linux%20ci_yaml%20engine%20roller/18/overview

There's no stdout or stderr just the error code 254.

@CaseyHillers @flar 