When entering PIP with multi-activity, re-use mLastNonFullscreenBounds.

In freeform support, we use mLastNonFullScreenBounds to keep track of
the task's bounds in freeform. Such that when maximizing/entering PIP, it
can restore to this bound after un-maximize/exiting PIP.

However when creating a new stack (in the case of multiple-activity in
the task, such as VLC), this information gets lost. We will reuse the
current task's lastNonfullscreenBounds.

Bug: 156780576
Test: In freeform, enter PIP using Multi-activity PIP (e.g. VLC), expand
PIP, the PIP activity is using the same bounds as before

Change-Id: Ic633fd1704c6e909fef0c2bd2dfe4bd9e2ca53ae

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

@@ -2176,6 +2176,10 @@ class RootWindowContainer extends WindowContainer<DisplayContent>
                 // move the PIP activity into the task.
                 stack = taskDisplayArea.createStack(WINDOWING_MODE_UNDEFINED, r.getActivityType(),
                         ON_TOP, r.info, r.intent, false /* createdByOrganizer */);
+                // It's possible the task entering PIP is in freeform, so save the last
+                // non-fullscreen bounds. Then when this new PIP task exits PIP, it can restore
+                // to its previous freeform bounds.
+                stack.setLastNonFullscreenBounds(task.mLastNonFullscreenBounds);
 
                 // There are multiple activities in the task and moving the top activity should
                 // reveal/leave the other activities in their original task.