GitLab

Register a log message handler in BrowserTestBase if --enable-tracing is
passed and flush the trace when encountering a fatal message.

R=eseckler@chromium.org,skyostil@chromium.org,nasko@chromium.org
BUG=1157954

Change-Id: Ic28b108e9b15a38e4f2c94a4a713583b98fa1998
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2595384
Commit-Queue: Alexander Timin <altimin@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841452}