Disable flaky UpdateWindowSizeExitsFullscreen test.

Fails flakily on Mac 10.7.

Flakiness dashboard:  http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40ToT%20Chromium&testType=interactive_ui_tests&tests=ExtensionApiTest.UpdateWindowSizeExitsFullscreen

Build log: http://build.chromium.org/p/chromium.mac/buildstatus?builder=Mac10.7%20Tests%20%281%29&number=17016

BUG=308041
TBR=jyasskin

Review URL: https://codereview.chromium.org/27520002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228912 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228912