Merge "Explain why MAX_RUNNING_USERS is 3."

class UserController implements Handler.Callback {

    private static final String TAG = TAG_WITH_CLASS_NAME ? "UserController" : TAG_AM;

    // Maximum number of users we allow to be running at a time.

    /**

     * Maximum number of users we allow to be running at a time, including the system user and

     * its profiles.

     * Note changing this to 2 is not recommended, since that would mean, if the user uses

     * work profile and then switch to a secondary user, then the work profile user would be killed,

     * which should work fine, but aggressively killing the work profile user that has just been

     * running could cause data loss.  (Even without work profile, witching from secondary user A

     * to secondary user B would cause similar issues on user B.)

     *

     * TODO: Consider adding or replacing with "MAX_RUNNING_*SECONDARY*_USERS", which is the max

     * number of running *secondary, switchable* users.

     */

    static final int MAX_RUNNING_USERS = 3;

    // Amount of time we wait for observers to handle a user switch before