ui/aura: Add missing dep for xdisplaycheck.
ui/aura: Add missing dep for xdisplaycheck.

xdisplaycheck is a runtime dependency that should be present when running
under isolate.

I found this while investigating the problem with extensions_unittests
under  http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_clobber_rel_ng/builds/46357/steps/compile%20%28without%20patch%29/logs/stdio

BUG=None
R=maruel@chromium.org
TBR=sadrul@chromium.org

Review URL: https://codereview.chromium.org/1256983004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#340418}

ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend,CapOM/ChromiumGStreamerBackend,ltilve/ChromiumGStreamerBackend