Fix overexpand panel motion

Expanding was already set to false when we decided which QS
overscroll animation to run. We can't change the order of expanding
finished/tracking finished because of another bug. Instead, let the
stack scroller know about tracking state and combine both of them.

Bug: 21705230
Change-Id: I041ff1fabc6c939c233528f9d08d804ead64bbab
diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/phone/NotificationPanelView.java b/packages/SystemUI/src/com/android/systemui/statusbar/phone/NotificationPanelView.java
index 5078b5c..c89a37d 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/phone/NotificationPanelView.java
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/phone/NotificationPanelView.java
@@ -1818,6 +1818,7 @@
                 || mStatusBar.getBarState() == StatusBarState.SHADE_LOCKED) {
             mAfforanceHelper.animateHideLeftRightIcon();
         }
+        mNotificationStackScroller.onPanelTrackingStarted();
     }
 
     @Override
@@ -1827,6 +1828,7 @@
             mNotificationStackScroller.setOverScrolledPixels(
                     0.0f, true /* onTop */, true /* animate */);
         }
+        mNotificationStackScroller.onPanelTrackingStopped();
         if (expand && (mStatusBar.getBarState() == StatusBarState.KEYGUARD
                 || mStatusBar.getBarState() == StatusBarState.SHADE_LOCKED)) {
             if (!mHintAnimationRunning) {