chromeos: fix bug where "aw snap" page replaces first tab if it was a NTP when closing window with > 1 tab.

BUG=chromium-os:12088
TEST=verify bug per bug report.
Review URL: http://codereview.chromium.org/6882058

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@83031 0039d316-1c4b-4281-b951-d872f2087c98
void TabStripModel::SelectRelativeTab(bool next) {
  if (contents_data_.empty())
    return;

  int index = active_index();
  int delta = next ? 1 : -1;
  index = (index + count() + delta) % count();
  ActivateTabAt(index, true);
}

void TabStripModel::SelectRelativeTab(bool next) {
  if (contents_data_.empty())
    return;

  int index = active_index();
  int delta = next ? 1 : -1;
  index = (index + count() + delta) % count();
  ActivateTabAt(index, true);
}
