Ensuring that fast scrolling to predictions scrolls list to the top

- Fixes a long standing issue with fast-scrolling to the predicted apps
  not quite scrolling the list to the top of the screen.
- Fixes an issue where we don’t scroll exactly to the fast scroll 
  position due to rounding
- Also fixes a small issue where the thumb would not update when the 
  fast scroll popup was no longer showing, even while dragging.

Bug: 30023608

Change-Id: I6b5080c6aea521ff03dca24317f0405c02725061

src/com/android/launcher3/BaseRecyclerViewFastScrollBar.java

@@ -156,10 +156,6 @@ public class BaseRecyclerViewFastScrollBar {
         return mThumbMaxWidth;
     }
 
-    public float getLastTouchY() {
-        return mLastTouchY;
-    }
-
     public boolean isDraggingThumb() {
         return mIsDragging;
     }
@@ -210,6 +206,7 @@ public class BaseRecyclerViewFastScrollBar {
                     mPopup.animateVisibility(!sectionName.isEmpty());
                     mRv.invalidate(mPopup.updateFastScrollerBounds(lastY));
                     mLastTouchY = boundedY;
+                    setThumbOffset(mRv.getScrollBarX(), (int) mLastTouchY);
                 }
                 break;
             case MotionEvent.ACTION_UP: