This helps isolate particular debug log messages to specific tests.

BUG=angleproject:667

Change-Id: I6be37d50cc41a13abbceb395e6e9b603bd44c7bd
Reviewed-on: https://chromium-review.googlesource.com/316611
Tryjob-Request: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>