Unify NewTabPageItem and ItemGroup into a single tree-structured interface.

chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/StatusItem.java

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package org.chromium.chrome.browser.ntp.cards;
 
 import android.content.Context;
 import android.support.annotation.StringRes;
 
 import org.chromium.chrome.R;
 
 /**
  * Card that is shown when the user needs to be made aware of some information about their
  * configuration that affects the NTP suggestions.
  */
-public abstract class StatusItem implements NewTabPageItem, StatusCardViewHolder.DataSource {
+public abstract class StatusItem extends Leaf implements StatusCardViewHolder.DataSource {
     public static StatusItem createNoSuggestionsItem(SuggestionsCategoryInfo categoryInfo) {
         return new NoSuggestionsItem(categoryInfo);
     }
 
     private static class NoSuggestionsItem extends StatusItem {
         private final SuggestionsCategoryInfo mCategoryInfo;
 
         public NoSuggestionsItem(SuggestionsCategoryInfo info) {
             mCategoryInfo = info;
         }
@@ skipping 16 matching lines @@
             return 0;
         }
 
         @Override
         public void performAction(Context context) {
             assert false;
         }
     }
 
     @Override
-    public int getType() {
-        return NewTabPageItem.VIEW_TYPE_STATUS;
+    @ItemViewType
+    protected int getItemViewType() {
+        return ItemViewType.VIEW_TYPE_STATUS;
     }
 
     @Override
-    public void onBindViewHolder(NewTabPageViewHolder holder) {
+    protected void onBindViewHolder(NewTabPageViewHolder holder) {
         assert holder instanceof StatusCardViewHolder;
         ((StatusCardViewHolder) holder).onBindViewHolder(this);
     }
 }