Do not start two Xvfb when running web tests

run_web_tests.py manages Xvfb itself, so there is no need to pass the
`--xvfb` flag to run_isolated_script_test.py.

With this change, we should see "Starting Xvfb with display ":99""
(instead of ":100") in the Swarming output for webkit_layout_tests, as
there is no redundant Xvfb running on :99 any more.

Change-Id: Ifcd9afcf3f0150b7cfde70171bc19ca215277a99
Reviewed-on: https://chromium-review.googlesource.com/c/1405694
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621813}
1 file changed