[Mac] Don't disable all menu items if there isn't a browser window open.
[Mac] Don't disable all menu items if there isn't a browser window open.

BUG=46355
TEST=Close all browser windows. New Tab, New Window, History and Bookmark menus, etc are enabled.

Review URL: http://codereview.chromium.org/2767012

git-svn-id: http://src.chromium.org/svn/trunk/src@49536 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 02e7029ce47f1c41eacfe27b2297a9d17b341da8
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser