Fixes few corner issues of multi-window windowing mode split-screen

- Updates the preferred top focused root task when a root task was
  added on top.

- Also updates the resumed activity (so as the focused app) while
  root task position changed.

- Do not resume the top activities of the tasks that are visible, but is
  behind other visible tasks (TASK_VISIBILITY_VISIBLE_BEHIND_TRANSLUCENT).

Bug: 177190100
Test: ActivityLifecycleLegacySplitScreenTests
Test: MultiWindowTests#testLaunchToSideAndBringToFront
Change-Id: Ied5041f3987a964931cdab508955759671336af4

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

@@ -6060,12 +6060,10 @@ class Task extends WindowContainer<WindowContainer> {
                 int idx = mChildren.size() - 1;
                 while (idx >= 0) {
                     final Task child = (Task) getChildAt(idx--);
-                    if (!child.isFocusableAndVisible()) {
-                        break;
+                    if (!child.isTopActivityFocusable()) {
+                        continue;
                     }
-
-                    // Only allow one activity to be resumed among sibling tasks in split-screen.
-                    if (inSplitScreenWindowingMode() && someActivityResumed) {
+                    if (child.getVisibility(null /* starting */) != TASK_VISIBILITY_VISIBLE) {
                         break;
                     }
 

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

@@ -346,6 +346,12 @@ final class TaskDisplayArea extends DisplayArea<WindowContainer> {
         position = findPositionForRootTask(position, task, true /* adding */);
 
         super.addChild(task, position);
+        if (mPreferredTopFocusableRootTask != null
+                && task.isFocusable()
+                && mPreferredTopFocusableRootTask.compareTo(task) < 0) {
+            // Clear preferred top because the adding focusable task has a higher z-order.
+            mPreferredTopFocusableRootTask = null;
+        }
         mAtmService.updateSleepIfNeededLocked();
         onRootTaskOrderChanged(task);
     }
@@ -439,6 +445,11 @@ final class TaskDisplayArea extends DisplayArea<WindowContainer> {
         // Update the top resumed activity because the preferred top focusable task may be changed.
         mAtmService.mTaskSupervisor.updateTopResumedActivityIfNeeded();
 
+        final ActivityRecord r = child.getResumedActivity();
+        if (r != null && r == mRootWindowContainer.getTopResumedActivity()) {
+            mAtmService.setResumedActivityUncheckLocked(r, "positionChildAt");
+        }
+
         if (mChildren.indexOf(child) != oldPosition) {
             onRootTaskOrderChanged(child);
         }

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

@@ -2157,6 +2157,8 @@ public class ActivityRecordTests extends WindowTestsBase {
         attrs.setTitle("AppWindow");
         final TestWindowState appWindow = createWindowState(attrs, activity);
         activity.addWindow(appWindow);
+        spyOn(appWindow);
+        doNothing().when(appWindow).onStartFreezingScreen();
 
         // Set initial orientation and update.
         activity.setOrientation(SCREEN_ORIENTATION_LANDSCAPE);
@@ -2193,6 +2195,8 @@ public class ActivityRecordTests extends WindowTestsBase {
         attrs.setTitle("RotationByPolicy");
         final TestWindowState appWindow = createWindowState(attrs, activity);
         activity.addWindow(appWindow);
+        spyOn(appWindow);
+        doNothing().when(appWindow).onStartFreezingScreen();
 
         // Set initial orientation and update.
         performRotation(displayRotation, Surface.ROTATION_90);