Annotate leak of a Screen instance in system display API tests.

BUG=313707
R=hongbo.min@intel.com
TBR=hongbo.min@intel.com
TEST=browser_tests:SystemDisplayAPI*

Review URL: https://codereview.chromium.org/59693002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233574 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233574