Fix split screen divider corners flicker

Divider bar might be hidden before swipe-up gesture started when users
touching task bar region. This makes sure to update visibility of
divider bar only after gesture started.

Fix: 219995626
Test: long press task bar region to stash/unstash task bar, divider bar
      won't be hidden as long as it didn't trigger swipe up gesture.
Change-Id: Iacf690c84a3ad4b5e4fc9b066e9a1ecb8a8aa7d1
diff --git a/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java b/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java
index 2cb7100..9c28bce 100644
--- a/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java
+++ b/quickstep/src/com/android/quickstep/AbsSwipeUpHandler.java
@@ -833,12 +833,9 @@
         // Notify when the animation starts
         flushOnRecentsAnimationAndLauncherBound();
 
-        // Start hiding the divider
-        setDividerShown(false /* shown */, false /* immediate */);
-
         // Only add the callback to enable the input consumer after we actually have the controller
         mStateCallback.runOnceAtState(STATE_APP_CONTROLLER_RECEIVED | STATE_GESTURE_STARTED,
-                mRecentsAnimationController::enableInputConsumer);
+                this::startInterceptingTouchesForGesture);
         mStateCallback.setStateOnUiThread(STATE_APP_CONTROLLER_RECEIVED);
 
         mPassedOverviewThreshold = false;
@@ -1457,6 +1454,17 @@
         return swipePipToHomeAnimator;
     }
 
+    private void startInterceptingTouchesForGesture() {
+        if (mRecentsAnimationController == null) {
+            return;
+        }
+
+        mRecentsAnimationController.enableInputConsumer();
+
+        // Start hiding the divider
+        setDividerShown(false /* shown */, true /* immediate */);
+    }
+
     private void computeRecentsScrollIfInvisible() {
         if (mRecentsView != null && mRecentsView.getVisibility() != View.VISIBLE) {
             // Views typically don't compute scroll when invisible as an optimization,