Fix flakiness of testTransferLaunchCookie

The count down latch is triggered too early that the value
to be verified may not have been set.

Fixes: 194183975
Test: atest ActivityOptionsTest#testTransferLaunchCookie
Change-Id: I3b78db921a178e2df970a85496ae5238b5bd6fb3
(cherry picked from commit c10eb7b18d)

services/tests/wmtests/src/com/android/server/wm/ActivityOptionsTest.java

@@ -110,18 +110,20 @@ public class ActivityOptionsTest {
             @Override
             public void onTaskAppeared(RunningTaskInfo taskInfo, SurfaceControl leash) {
                 try (SurfaceControl.Transaction t = new SurfaceControl.Transaction()) {
-                    t.setVisibility(leash, true /* visible */).apply();
+                    t.show(leash).apply();
                 }
                 int cookieIndex = -1;
                 if (trampoline.equals(taskInfo.baseActivity)) {
                     cookieIndex = 0;
                 } else if (main.equals(taskInfo.baseActivity)) {
                     cookieIndex = 1;
-                    mainLatch.countDown();
                 }
                 if (cookieIndex >= 0) {
                     appearedCookies[cookieIndex] = taskInfo.launchCookies.isEmpty()
                             ? null : taskInfo.launchCookies.get(0);
+                    if (cookieIndex == 1) {
+                        mainLatch.countDown();
+                    }
                 }
             }
         };