Re-enable display_unittests for the Ozone ChromiumOS bot

display_unittests were fixed for Ozone in https://codereview.chromium.org/383463002/

BUG=none
NOTRY=true

Review URL: https://codereview.chromium.org/388483003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@282358 0039d316-1c4b-4281-b951-d872f2087c98

testing/buildbot/chromium.chromiumos.json

@@ -57,6 +57,7 @@
       "components_unittests",
       "crypto_unittests",
       "dbus_unittests",
+      "display_unittests",
       "gcm_unit_tests",
       "google_apis_unittests",
       "gpu_unittests",