Remove TabContents from TabStripModelObserver::TabDetachedAt.

BUG=107201
TEST=no visible change


Review URL: https://chromiumcodereview.appspot.com/11293205

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@167122 0039d316-1c4b-4281-b951-d872f2087c98
void TabStripModel::ActivateTabAt(int index, bool user_gesture) {
  DCHECK(ContainsIndex(index));
  TabStripSelectionModel new_model;
  new_model.Copy(selection_model_);
  new_model.SetSelectedIndex(index);
  SetSelection(new_model, user_gesture ? NOTIFY_USER_GESTURE : NOTIFY_DEFAULT);
}

void TabStripModel::ActivateTabAt(int index, bool user_gesture) {
  DCHECK(ContainsIndex(index));
  TabStripSelectionModel new_model;
  new_model.Copy(selection_model_);
  new_model.SetSelectedIndex(index);
  SetSelection(new_model, user_gesture ? NOTIFY_USER_GESTURE : NOTIFY_DEFAULT);
}
