Waiting for the drop bar to go away after dragging an icon

This should remove test flakes like: https://sponge.corp.google.com/target?show=FAILED&sortBy=STATUS&id=2c560d05-9d50-4fad-9798-dc77858f2d11&target=com.android.launcher3.tests

Test: AOSP TAPL tests
Change-Id: I01899bec349ed507a03fd02196a35990c48fd46b

tests/tapl/com/android/launcher3/tapl/LauncherInstrumentation.java

@@ -350,7 +350,7 @@ public final class LauncherInstrumentation {
         return new AllAppsFromOverview(this);
     }
 
-    private void waitUntilGone(String resId) {
+    void waitUntilGone(String resId) {
         assertTrue("Unexpected launcher object visible: " + resId,
                 mDevice.wait(Until.gone(getLauncherObjectSelector(resId)),
                         WAIT_TIME_MS));

tests/tapl/com/android/launcher3/tapl/Workspace.java

@@ -115,6 +115,7 @@ public final class Workspace extends Home {
         final Point dest = new Point(
                 mLauncher.getDevice().getDisplayWidth(), workspace.getVisibleBounds().centerY());
         app.getObject().drag(dest, ICON_DRAG_SPEED);
+        mLauncher.waitUntilGone("drop_target_bar");
         verifyActiveContainer();
     }