Fix issue with PiP hiding when dragging divider.

- Prevent the PiP windows from being set to drag resizing and getting
  clipped.

Test: Open PiP, dock a window, and start interacting with the divider.
Change-Id: I6a28a139261f1c3c09ec2b027e438df0411987c1

core/java/android/app/ActivityManager.java

@@ -697,6 +697,13 @@ public class ActivityManager {
                     && stackId != DOCKED_STACK_ID && stackId != PINNED_STACK_ID;
         }
 
+        /**
+         * Returns true if the input stack is affected by drag resizing.
+         */
+        public static boolean isStackAffectedByDragResizing(int stackId) {
+            return isStaticStack(stackId) && stackId != PINNED_STACK_ID;
+        }
+
         /**
          * Returns true if the windows of tasks being moved to the target stack from the source
          * stack should be replaced, meaning that window manager will keep the old window around

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

@@ -3198,8 +3198,10 @@ class WindowState extends WindowContainer<WindowState> implements WindowManagerP
         if (task == null) {
             return false;
         }
+        if (!StackId.isStackAffectedByDragResizing(getStackId())) {
+            return false;
+        }
         if (mAttrs.width != MATCH_PARENT || mAttrs.height != MATCH_PARENT) {
-
             // Floating windows never enter drag resize mode.
             return false;
         }