Fix two dragging related bugs in Launcher home

- accessibility bug: 199394124
- dragging on side bug: http://shortn/_LFBdIllupk

Test: manual
Bug: 199394124
Change-Id: I478e31332119f337bf0f8b6c92926845eb4889c4
diff --git a/src/com/android/launcher3/PagedView.java b/src/com/android/launcher3/PagedView.java
index 2f9b5af..978886d 100644
--- a/src/com/android/launcher3/PagedView.java
+++ b/src/com/android/launcher3/PagedView.java
@@ -1553,7 +1553,7 @@
         return getDisplacementFromScreenCenter(childIndex, screenCenter);
     }
 
-    private int getScreenCenter(int primaryScroll) {
+    protected int getScreenCenter(int primaryScroll) {
         float primaryScale = mOrientationHandler.getPrimaryScale(this);
         float primaryPivot =  mOrientationHandler.getPrimaryValue(getPivotX(), getPivotY());
         int pageOrientationSize = mOrientationHandler.getMeasuredSize(this);