[reland] Do not set default wallpaper unless it should do so.

TBR=bshe@chromium.org, alemate@chromium.org

Bug: 751382
Change-Id: Id0793dfe467f737526a95b1e66ed01fbb8860bda
Reviewed-on: https://chromium-review.googlesource.com/619754
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Reviewed-by: Biao She <bshe@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#498325}
Reviewed-on: https://chromium-review.googlesource.com/646430
Cr-Commit-Position: refs/heads/master@{#498982}
int FindPublicSession(const user_manager::UserList& users) {
  int index = -1;
  int i = 0;
  for (user_manager::UserList::const_iterator it = users.begin();
       it != users.end();
       ++it, ++i) {
    if ((*it)->GetType() == user_manager::USER_TYPE_PUBLIC_ACCOUNT) {
      index = i;
      break;
    }
  }

  return index;
}

int FindPublicSession(const user_manager::UserList& users) {
  int index = -1;
  int i = 0;
  for (user_manager::UserList::const_iterator it = users.begin();
       it != users.end();
       ++it, ++i) {
    if ((*it)->GetType() == user_manager::USER_TYPE_PUBLIC_ACCOUNT) {
      index = i;
      break;
    }
  }

  return index;
}
