Xvfb is needed for the screen capture tests in modules_unittests, which also brings in xdisplaycheck used by testing/xvfb.py. libjingle_media_unittest was missing a resource video in the .isolate file. BUG=chromium:497757 R=stip@chromium.org Review URL: https://codereview.webrtc.org/1415603005 . Cr-Commit-Position: refs/heads/master@{#10365}