Fix create profile dialog display bug.

When using zoom level 90%, there was some issue
with the profile icon grid that the last profile
in each line was moved to another line. This CL
adds back some bottom margin which was removed
earlier to fix this.

BUG=335512
TEST=open create profile dialog with zoom level 90%

Review URL: https://codereview.chromium.org/141163010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245691 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245691