Mac: Menu bar not hidden in immersive fullscreen mode.

When a window is on a secondary screen, and "Displays have separate spaces"
option is turned on, the menu bar is not hidden during immersive fullscreen
mode. The problem was that the logic to hide the menu bar was incorrectly
determining whether the screen had a menu bar.

After fixing the logic, I also had to introduce a minor hack to counteract the
"helpfulness" of AppKit. See http://crbug.com/403203 for further details.

BUG=396980

Review URL: https://codereview.chromium.org/467093002

git-svn-id: http://src.chromium.org/svn/trunk/src/base@290598 4ff67af0-8c30-449e-8e8b-ad334ec8d88c