Generate folder icon with the top 4 child items' icon tiled in 2x2 grid.

BUG=303211

Review URL: https://codereview.chromium.org/26626006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228331 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228331