Originally the initialization of window button's is done in FileManager
class. To keep FileManager class small, this CL moves the initialization to the
UI class.

BUG=267281
TEST=manually
R=mtomasz@chromium.org

Review URL: https://codereview.chromium.org/25992002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227265 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227265