Skip DisplayManagerTest.ScreenAfterShutdown on win8 (which doesn't support multiple dislpays on ash)

BUG=NONE
RDANBEAM

R=dbeam@chromium.org

Review URL: https://codereview.chromium.org/142003003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245578 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245578