Looking back in chat, it looks like Aaron would like for only the bytes of control messages to be logged.

Aaron and I discussed this more offline, and it seems like just disabling the logging of data frames in favor of just logging the number of bytes received in the data frames will also work. The reason for this is that, if we log all of the bytes received in the frame, then it takes long enough that it exacerbates the problem where we can't read bytes off the wire fast enough and thus drop bytes. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4a4dbdadd4632038295e2e5133b7f3a162c78f27

commit 4a4dbdadd4632038295e2e5133b7f3a162c78f27
Author: charliea <charliea@chromium.org>
Date: Wed Aug 10 15:50:10 2016

[battor agent] Don't log all bytes received when reading sample frames

This logging mode exacerbates problems on Mac wherein we drop sample
frames because the serial buffer overflows from not processing frames
fast enough.

TBR=aschulman@chromium.org
BUG= 636167 

Review-Url: https://codereview.chromium.org/2233893002
Cr-Commit-Position: refs/heads/master@{#411047}

[modify] https://crrev.com/4a4dbdadd4632038295e2e5133b7f3a162c78f27/tools/battor_agent/battor_connection_impl.cc