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

chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/ProgressViewHolder.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.view.LayoutInflater;
 
 import org.chromium.chrome.R;
 
 /**
- * ViewHolder for an item of type {@link NewTabPageItem#VIEW_TYPE_PROGRESS}.
+ * ViewHolder for an item of type {@link ItemViewType#PROGRESS}.
  * Adds a {@link ProgressIndicatorView} to the recycler view.
  */
 public class ProgressViewHolder extends NewTabPageViewHolder {
     private final ProgressIndicatorView mProgressIndicator;
     private ProgressItem mListItem;
 
     public ProgressViewHolder(final NewTabPageRecyclerView recyclerView) {
         super(LayoutInflater.from(recyclerView.getContext())
                         .inflate(R.layout.new_tab_page_progress_indicator, recyclerView, false));
         mProgressIndicator = (ProgressIndicatorView) itemView.findViewById(R.id.snippets_progress);
     }
 
     public void onBindViewHolder(ProgressItem item) {
         mListItem = item;
         updateDisplay();
     }
 
     public void updateDisplay() {
         if (mListItem.isVisible()) {
             mProgressIndicator.showDelayed();
         } else {
             mProgressIndicator.hide();
         }
     }
 }