Fix ActivityOption#setTaskOverlay can be covered by other activity.

Although ActivityRecord#setTaskOverlay has set setAlwaysOnTop, but it
is not useful in Task#getAdjustedChildPosition, because when sorting
activities in a task, it is meanless to check the windowing mode for
an activity. A simple solution is to override the isAlwaysOnTop method.

And because Task#showToCurrentUser will depends on current top task,
so we cannot add the task before adjusting the position.

Bug: 181721787
Test: atest RootTaskTests StartActivityAsUserTests StartActivityTests
Change-Id: I7fdf19d04bf71fa97a841223c06fad9a7e0b2ee4

services/core/java/com/android/server/wm/ActivityRecord.java

@@ -8242,6 +8242,11 @@ final class ActivityRecord extends WindowToken implements WindowManagerService.A
         return mTaskOverlay;
     }
 
+    @Override
+    public boolean isAlwaysOnTop() {
+        return mTaskOverlay || super.isAlwaysOnTop();
+    }
+
     @Override
     boolean showToCurrentUser() {
         return mShowForAllUsers || mWmService.isCurrentProfile(mUserId);

services/core/java/com/android/server/wm/Task.java

@@ -3150,11 +3150,14 @@ class Task extends WindowContainer<WindowContainer> {
 
         // Figure-out min/max possible position depending on if child can show for current user.
         int minPosition = (canShowChild) ? computeMinUserPosition(0, size) : 0;
-        int maxPosition = (canShowChild) ? size : computeMaxUserPosition(size - 1);
+        int maxPosition = (canShowChild) ? size - 1 : computeMaxUserPosition(size - 1);
+        if (!hasChild(wc)) {
+            // Increase the maxPosition because children size will grow once wc is added.
+            ++maxPosition;
+        }
 
         // Factor in always-on-top children in max possible position.
         if (!wc.isAlwaysOnTop()) {
-
             // We want to place all non-always-on-top containers below always-on-top ones.
             while (maxPosition > minPosition) {
                 if (!mChildren.get(maxPosition - 1).isAlwaysOnTop()) break;