This adds 3 new profiler markers for each IPC message:
* One just before the first byte is sent over the IPC channel
* One just after the last byte is sent over the IPC channel
* One just after the last byte is received from the IPC channel
With the already-existing IPC markers (for when SendXXX and RecvXXX are
called), this allows us to calculate the following statistics:
* Send thread latency
* IPC send duration
* IPC recv latency
* Recv thread latency
For more information on how this is presented in the UI, see:
<https://github.com/firefox-devtools/profiler/pull/2535>.
Differential Revision: https://phabricator.services.mozilla.com/D70790
632c7aa9aa