Fix empty stacks leaked after blocking background activity launches.

Background activity starts were blocked while stacks were created
and leaked.

Remove the stack if the activity failed to launch and no activities
left in the stack. Also avoid creating new stack for the blocked
background activity which is unnecessary.

Bug: 134016361
Test: atest BackgroundActivityLaunchTest

Change-Id: Ifa04a9062cb771929a9614cc164fd64b3f60edf1

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

@@ -1419,6 +1419,13 @@ class ActivityStarter {
                     stack.finishActivityLocked(mStartActivity, RESULT_CANCELED,
                             null /* intentResultData */, "startActivity", true /* oomAdj */);
                 }
+
+                // Stack should also be detached from display and be removed if it's empty.
+                if (startedActivityStack != null && startedActivityStack.isAttached()
+                        && startedActivityStack.numActivities() == 0
+                        && !startedActivityStack.isActivityTypeHome()) {
+                    startedActivityStack.remove();
+                }
             }
             mService.mWindowManager.continueSurfaceLayout();
         }
@@ -2289,15 +2296,17 @@ class ActivityStarter {
     }
 
     private int setTaskFromReuseOrCreateNewTask(TaskRecord taskToAffiliate) {
+        if (mRestrictedBgActivity && (mReuseTask == null || !mReuseTask.containsAppUid(mCallingUid))
+                && handleBackgroundActivityAbort(mStartActivity)) {
+            return START_ABORTED;
+        }
+
         mTargetStack = computeStackFocus(mStartActivity, true, mLaunchFlags, mOptions);
 
         // Do no move the target stack to front yet, as we might bail if
         // isLockTaskModeViolation fails below.
 
         if (mReuseTask == null) {
-            if (mRestrictedBgActivity && handleBackgroundActivityAbort(mStartActivity)) {
-                return START_ABORTED;
-            }
             final TaskRecord task = mTargetStack.createTaskRecord(
                     mSupervisor.getNextTaskIdForUserLocked(mStartActivity.mUserId),
                     mNewTaskInfo != null ? mNewTaskInfo : mStartActivity.info,
@@ -2310,11 +2319,6 @@ class ActivityStarter {
             if (DEBUG_TASKS) Slog.v(TAG_TASKS, "Starting new activity " + mStartActivity
                     + " in new task " + mStartActivity.getTaskRecord());
         } else {
-            if (mRestrictedBgActivity && !mReuseTask.containsAppUid(mCallingUid)) {
-                if (handleBackgroundActivityAbort(mStartActivity)) {
-                    return START_ABORTED;
-                }
-            }
             addOrReparentStartingActivity(mReuseTask, "setTaskFromReuseOrCreateNewTask");
         }