Show shadow when entity header starts scrolling.

- Add a controller to manage add/remove onScrollChangedListener to
  recyclerviews.
- When recyclerview on each screen is scrolled to top, set actionbar
  elevation to 0, otherwise set it to non-zero.
- When screen is moved to background, detach the listener.
- Use the controller in entity header.

Change-Id: Iecf194d885098c98c392810f62893ae9189f3936
Fix: 37670670
Test: make RunSettingsRoboTests

src/com/android/settings/datausage/AppDataUsage.java

@@ -327,6 +327,7 @@ public class AppDataUsage extends DataUsageBase implements Preference.OnPreferen
         final Activity activity = getActivity();
         final Preference pref = EntityHeaderController
                 .newInstance(activity, this, null /* header */)
+                .setRecyclerView(getListView(), getLifecycle())
                 .setButtonActions(showInfoButton
                                 ? EntityHeaderController.ActionType.ACTION_APP_INFO
                                 : EntityHeaderController.ActionType.ACTION_NONE,