Show footer buttons ("upload" and "cancel") for upload-folder dialog.

BUG=321093

Review URL: https://codereview.chromium.org/77813002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236226 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236226