Instead, we can just concatenate the records together, which means you can view
the generated trace file without post-processing. Also, I've made the trace
file world-readable, so that you can trace a device without needing root
access.
This updates to mojo commit d259eb58aa59 and limits the roll script to
only pull in the parts of //mojo that are currently being used. More
stuff will be dropped in the future.