Adding support for top padding in BaseRecyclerView. The scrollbar is

drawn below the top padding.
Also adding callback for getting the all-apps vertical pull range
so that it can be controlled by SearchUiManager

Bug: 37616877
Change-Id: Ib4642073f3e92f6676caede3bddd652fda89c86f

src/com/android/launcher3/allapps/SearchUiManager.java

@@ -55,4 +55,14 @@ public interface SearchUiManager {
      * TODO: Remove when removing support for opening all-apps in search mode.
      */
     void startAppsSearch();
+
+    void addOnScrollRangeChangeListener(OnScrollRangeChangeListener listener);
+
+    /**
+     * Callback for listening to changes in the vertical scroll range when opening all-apps.
+     */
+    interface OnScrollRangeChangeListener {
+
+        void onScrollRangeChanged(int scrollRange);
+    }
 }