Merge "Update documentation for postmessage method"

     * messages to a certain target origin. See

     * <a href="https://html.spec.whatwg.org/multipage/comms.html#posting-messages">

     * HTML5 spec</a> for how target origin can be used.

     * <p>

     * A target origin can be set as a wildcard ("*"). However this is not recommended.

     * See the page above for security issues.

     *

     * @param message the WebMessage

     * @param targetOrigin the target origin. This is the origin of the page

     *          that is intended to receive the message. For best security

     *          practices, the user should not specify a wildcard (*) when

     *          specifying the origin.

     * @param targetOrigin the target origin.

     */

    public void postWebMessage(WebMessage message, Uri targetOrigin) {

        checkThread();