Mac: Improve behavior of "Add Folder" contextual menu item.
Mac: Improve behavior of "Add Folder" contextual menu item.

* "Add Folder" on a current folder now inserts the new folder as the last child of the parent folder rather than it's sibling.
* "Add Folder" on the "others" folder works as above.

This matches Windows behavior.
BUG=40722
TEST=See bug.

Review URL: http://codereview.chromium.org/1659003

git-svn-id: http://src.chromium.org/svn/trunk/src@44650 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 37bebeadd8b0488ed45e694fc2762a81a91b1bfa
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