views: Move button directory to ui/views/controls/.
BUG=104039
R=maruel@chromium.org
TBR=ben@chromium.org
Review URL: http://codereview.chromium.org/8716001
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@111669 0039d316-1c4b-4281-b951-d872f2087c98