Merge "Discourage Handler has/remove operations" into main

 * the same <em>post</em> or <em>sendMessage</em> methods as before, but from

 * your new thread.  The given Runnable or Message will then be scheduled

 * in the Handler's message queue and processed when appropriate.

 *

 * <h2>Performance considerations when using {@code Handler}</h2>

 *

 * <p>Beware that the "has" and "remove" methods of {@code Handler} can be very

 * slow because these operations scan the entire queue of pending messages.

 * If the underlying {@link Looper}'s {@link MessageQueue} has many pending

 * messages, this can be expensive.

 *

 * <ul>

 * <li>Instead of removing a message or a callback to cancel a pending

 * operation, consider setting a flag to indicate cancellation and having the

 * operation check the flag before proceeding.

 * <li>Instead of checking if the queue has a message or a callback to find if

 * a pending operation has not yet occurred, consider having that operation set

 * a flag to indicate that it has begun.

 * </ul>

 *

 * See {@code java.util.concurrent} for standard concurrency primitives.

 */

@RavenwoodKeepWholeClass

@RavenwoodRedirectionClass("Handler_ravenwood")