Add OVERRIDE to ui::TreeModelObserver overridden methods.

BUG=None
TEST=None

R=sky@chromium.org

Review URL: http://codereview.chromium.org/7046093

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@88827 0039d316-1c4b-4281-b951-d872f2087c98
void TreeView::SetRootShown(bool root_shown) {
  if (root_shown_ == root_shown)
    return;
  root_shown_ = root_shown;
  if (!model_ || !tree_view_)
    return;
  DeleteRootItems();
  CreateRootItems();
}

void TreeView::SetRootShown(bool root_shown) {
  if (root_shown_ == root_shown)
    return;
  root_shown_ = root_shown;
  if (!model_ || !tree_view_)
    return;
  DeleteRootItems();
  CreateRootItems();
}
