Do not create window decorations for split roots

Split roots (either the single-top root or stage roots) were usually
excluded from having window decorations by the exclusion logic for
non-leafs that exists in FreeformTaskTransitionObserver. However,
once split is dismissed and the child tasks are reparented out of the
stages, the two stage roots become leafs and if they were included as
part of a transition, a window decoration was being created for each of
them. This change excludes split roots from having a window decoration.

Bug: 280499263
Test: enter split, dismiss split by dragging the divider, observe
there's no crash

Change-Id: I4d563176a75512232fc853232b3666d511e4c922

libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/SplitScreenController.java

@@ -337,6 +337,11 @@ public class SplitScreenController implements DragAndDropPolicy.Starter,
         return isTaskInSplitScreen(taskId) && isSplitScreenVisible();
     }
 
+    /** Check whether the task is the single-top root or the root of one of the stages. */
+    public boolean isTaskRootOrStageRoot(int taskId) {
+        return mStageCoordinator.isRootOrStageRoot(taskId);
+    }
+
     public @SplitPosition int getSplitPosition(int taskId) {
         return mStageCoordinator.getSplitPosition(taskId);
     }

libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageCoordinator.java

@@ -377,6 +377,13 @@ public class StageCoordinator implements SplitLayout.SplitLayoutHandler,
         return STAGE_TYPE_UNDEFINED;
     }
 
+    boolean isRootOrStageRoot(int taskId) {
+        if (mRootTaskInfo != null && mRootTaskInfo.taskId == taskId) {
+            return true;
+        }
+        return mMainStage.isRootTaskId(taskId) || mSideStage.isRootTaskId(taskId);
+    }
+
     boolean moveToStage(ActivityManager.RunningTaskInfo task, @SplitPosition int stagePosition,
             WindowContainerTransaction wct) {
         prepareEnterSplitScreen(wct, task, stagePosition);

libs/WindowManager/Shell/src/com/android/wm/shell/splitscreen/StageTaskListener.java

@@ -286,6 +286,10 @@ class StageTaskListener implements ShellTaskOrganizer.TaskListener {
         }
     }
 
+    boolean isRootTaskId(int taskId) {
+        return mRootTaskInfo != null && mRootTaskInfo.taskId == taskId;
+    }
+
     void onResizing(Rect newBounds, Rect sideBounds, SurfaceControl.Transaction t, int offsetX,
             int offsetY, boolean immediately) {
         if (mSplitDecorManager != null && mRootTaskInfo != null) {

libs/WindowManager/Shell/src/com/android/wm/shell/windowdecor/DesktopModeWindowDecorViewModel.java

@@ -760,6 +760,10 @@ public class DesktopModeWindowDecorViewModel implements WindowDecorViewModel {
 
     private boolean shouldShowWindowDecor(RunningTaskInfo taskInfo) {
         if (taskInfo.getWindowingMode() == WINDOWING_MODE_FREEFORM) return true;
+        if (mSplitScreenController.isPresent()
+                && mSplitScreenController.get().isTaskRootOrStageRoot(taskInfo.taskId)) {
+            return false;
+        }
         return DesktopModeStatus.isProto2Enabled()
                 && taskInfo.getActivityType() == ACTIVITY_TYPE_STANDARD
                 && mDisplayController.getDisplayContext(taskInfo.displayId)