Mac: fix tab closure problem when close tab buttons not shown.
Mac: fix tab closure problem when close tab buttons not shown.

BUG=26889
TEST=See bug description.

Review URL: http://codereview.chromium.org/373020

git-svn-id: http://src.chromium.org/svn/trunk/src@31347 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 6ea5290e242ce60abb66b196b8573bee35584c8a
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