This will let us override the util loader for all new traces. It will
also be easier to maintain going forward if we have to change the
header again.

The end goal is to run the trace tests with a custom GL layer that can
intercept certain API calls.

Bug: angleproject:4845
Change-Id: I028a1afdadf638998805d7b9a2cc6717cf5f0148
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2308029
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Cody Northrop <cnorthrop@google.com>