This restores the prior path where angle_enable_trace would let ANGLE
write a debug.txt file without needing environment variables or
run-time annotator attachments.

Bug: b/170249632
Change-Id: I28693f038572638eb6531c5bb8e42d6cc7a65451
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2523912Reviewed-by: Ian Elliott <ianelliott@google.com>
Commit-Queue: Ian Elliott <ianelliott@google.com>