[Mac] Enables drag N' drop for the buttons within the Browser Actions container. Also fixes an issue where the grippy was being shown when no Browser Actions were installed.
Known issue: You can drag the buttons outside of the container, even though they will recover by snapping back into place. This will be fixed in a further revision.

TEST=try dragging browser action buttons in order to reorder them.
BUG=26990
Review URL: http://codereview.chromium.org/1418003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@42845 0039d316-1c4b-4281-b951-d872f2087c98
5 files changed