Add '--xvfb' to telemetry_perf_unittests's args on linux-bionic-rel.

Bug: 1201723
Change-Id: Idaf1bccb5b3c59e0875a8c8850f3909b5eda906b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2847501
Commit-Queue: Ben Pastene <[email protected]>
Commit-Queue: John Chen <[email protected]>
Auto-Submit: Ben Pastene <[email protected]>
Reviewed-by: John Chen <[email protected]>
Cr-Commit-Position: refs/heads/master@{#875417}
diff --git a/testing/buildbot/test_suite_exceptions.pyl b/testing/buildbot/test_suite_exceptions.pyl
index dcf0094..210333b 100644
--- a/testing/buildbot/test_suite_exceptions.pyl
+++ b/testing/buildbot/test_suite_exceptions.pyl
@@ -2630,6 +2630,12 @@
         # TODO(crbug.com/1182948): Remove the experiment.
         'experiment_percentage': 100,
       },
+      'linux-bionic-rel': {
+        'args': [
+          '--xvfb',
+          '--jobs=1',
+        ],
+      },
       'linux-chromium-tests-staging-tests': {
         'args': [
           '--xvfb',