Merge "Update VpnService Javadoc to reflect new UX." into lmp-dev

 * conflict with each other. The system takes several actions to address

 * these issues. Here are some key points:

 * <ul>

 *   <li>User action is required to create a VPN connection.</li>

 *   <li>User action is required the first time an application creates a VPN

 *       connection.</li>

 *   <li>There can be only one VPN connection running at the same time. The

 *       existing interface is deactivated when a new one is created.</li>

 *   <li>A system-managed notification is shown during the lifetime of a

 * other methods in this class, and the right can be revoked at any time.

 * Here are the general steps to create a VPN connection:

 * <ol>

 *   <li>When the user press the button to connect, call {@link #prepare}

 *       and launch the returned intent.</li>

 *   <li>When the user presses the button to connect, call {@link #prepare}

 *       and launch the returned intent, if non-null.</li>

 *   <li>When the application becomes prepared, start the service.</li>

 *   <li>Create a tunnel to the remote server and negotiate the network

 *       parameters for the VPN connection.</li>

    /**

     * Prepare to establish a VPN connection. This method returns {@code null}

     * if the VPN application is already prepared. Otherwise, it returns an

     * if the VPN application is already prepared or if the user has previously

     * consented to the VPN application. Otherwise, it returns an

     * {@link Intent} to a system activity. The application should launch the

     * activity using {@link Activity#startActivityForResult} to get itself

     * prepared. The activity may pop up a dialog to require user action, and

     * it becomes prepared again, subsequent calls to other methods in this

     * class will fail.

     *

     * <p>The user may disable the VPN at any time while it is activated, in

     * which case this method will return an intent the next time it is

     * executed to obtain the user's consent again.

     *

     * @see #onRevoke

     */

    public static Intent prepare(Context context) {