Adding the function is very helpful for diagnostic messages. Also
change the name of the debug trace capture file to the more distinct
angle_debug.txt from debug.txt.

Change-Id: I59b3d61568fd3917cd8c4a8125ee1c28d608aa30
Reviewed-on: https://chromium-review.googlesource.com/321871
Tryjob-Request: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>