Add a button to bring back the action-bar if hidden.

BUG=333129
R=sergeyu@chromium.org

Review URL: https://codereview.chromium.org/135193005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248662 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248662