Fixes for fast-scrollbar when using work profile tabs in all apps.

- do not hide scrollbar between switching tabs
- full scrollbar height
- show predictionrow only when fully scrolled to top

Bug: 70037972
Bug: 68713881

Change-Id: Icaa434ce2726b75d22ec4ac3287ab2b0e18ce42b

src/com/android/launcher3/BaseRecyclerView.java

@@ -68,6 +68,7 @@ public abstract class BaseRecyclerView extends RecyclerView
         ViewGroup parent = (ViewGroup) getParent().getParent();
         mScrollbar = parent.findViewById(R.id.fast_scroller);
         mScrollbar.setRecyclerView(this, parent.findViewById(R.id.fast_scroller_popup));
+        onUpdateScrollbar(0);
     }
 
     /**
@@ -112,7 +113,7 @@ public abstract class BaseRecyclerView extends RecyclerView
      * Returns the height of the fast scroll bar
      */
     public int getScrollbarTrackHeight() {
-        return getHeight() - getScrollBarTop() - getPaddingBottom();
+        return mScrollbar.getHeight() - getScrollBarTop() - getPaddingBottom();
     }
 
     /**
@@ -130,12 +131,6 @@ public abstract class BaseRecyclerView extends RecyclerView
         return availableScrollBarHeight;
     }
 
-    @Override
-    protected void dispatchDraw(Canvas canvas) {
-        onUpdateScrollbar(0);
-        super.dispatchDraw(canvas);
-    }
-
     /**
      * Updates the scrollbar thumb offset to match the visible scroll of the recycler view.  It does
      * this by mapping the available scroll area of the recycler view to the available space for the