[OSX]  IMAGE_GRID macro for NinePartImage.

Mirrors Views' IMAGE_GRID macro, reducing boilerplate code.

BUG=none
R=rsesek@chromium.org

Review URL: https://codereview.chromium.org/160253005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251257 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251257