Don't try to auto-pip if there's already a pip

Was mistakenly not checking. Legacy just forbid this, so
do the same with shell.

Also, move when we reset track-count in wmcore. This is
not really consequential, but without it the logs are
a little less clear.

Bug: 280227595
Test: Swipe-to-home an auto-pip app while there is already
      a pip.
Change-Id: I95204309614bac523abdf9787ad668026d5d0401

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

@@ -954,6 +954,13 @@ class Transition implements BLASTSyncEngine.TransactionReadyListener {
                 // to the transient activity.
                 ar.supportsEnterPipOnTaskSwitch = true;
             }
+            // Make sure this activity can enter pip under the current circumstances.
+            // `enterPictureInPicture` internally checks, but with beforeStopping=false which
+            // is specifically for non-auto-enter.
+            if (!ar.checkEnterPictureInPictureState("enterPictureInPictureMode",
+                    true /* beforeStopping */)) {
+                return false;
+            }
             return mController.mAtm.enterPictureInPictureMode(ar, ar.pictureInPictureArgs,
                     false /* fromClient */);
         }

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

@@ -813,6 +813,10 @@ class TransitionController {
         }
         ProtoLog.v(ProtoLogGroup.WM_DEBUG_WINDOW_TRANSITIONS, "Finish Transition: %s", record);
         mPlayingTransitions.remove(record);
+        if (!inTransition()) {
+            // reset track-count now since shell-side is idle.
+            mTrackCount = 0;
+        }
         updateRunningRemoteAnimation(record, false /* isPlaying */);
         record.finishTransition();
         for (int i = mAnimatingExitWindows.size() - 1; i >= 0; i--) {
@@ -825,10 +829,9 @@ class TransitionController {
             }
         }
         mRunningLock.doNotifyLocked();
-        // Run state-validation checks when no transitions are active anymore.
+        // Run state-validation checks when no transitions are active anymore (Note: sometimes
+        // finish can start a transition, so check afterwards -- eg. pip).
         if (!inTransition()) {
-            // Can reset track-count now that everything is idle.
-            mTrackCount = 0;
             validateStates();
             mAtm.mWindowManager.onAnimationFinished();
         }