[thread_support.cc] Added a couple of helpful comments
[thread_support.cc] Added a couple of helpful comments

nkawahara/Graphite,nkawahara/Graphite,victorisildur/Graphite,victorisildur/Graphite,mit-carbon/Graphite,victorisildur/Graphite,mit-carbon/Graphite-Cycle-Level,mit-carbon/Graphite-Cycle-Level,fhijaz/Graphite,mit-carbon/Graphite,8l/Graphite,mit-carbon/Graphite-Cycle-Level,fhijaz/Graphite,nkawahara/Graphite,fhijaz/Graphite,8l/Graphite,mit-carbon/Graphite-Cycle-Level,8l/Graphite,victorisildur/Graphite,mit-carbon/Graphite,mit-carbon/Graphite,fhijaz/Graphite,8l/Graphite,nkawahara/Graphite