[Suggestions] Remove TreeNode.getSuggestionAt() in favor of a visitor.

chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/OptionalLeaf.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.support.annotation.CallSuper;
 
 import org.chromium.base.Callback;
-import org.chromium.chrome.browser.ntp.snippets.SnippetArticle;
 
 import java.util.Collections;
 import java.util.Set;
 
 /**
  * An optional leaf (i.e. single item) in the tree. Depending on its internal state (see
  * {@link #isVisible()}), the item will be present or absent from the tree, by manipulating the
  * values returned from {@link ChildNode} methods. This allows the parent node to not have to add or
  * remove the optional leaf from its children manually.
  *
@@ skipping 13 matching lines @@
         return getItemViewType();
     }
 
     @Override
     public void onBindViewHolder(NewTabPageViewHolder holder, int position) {
         checkIndex(position);
         onBindViewHolder(holder);
     }
 
     @Override
-    public SnippetArticle getSuggestionAt(int position) {
-        checkIndex(position);
-        return null;
-    }
-
-    @Override
     public Set<Integer> getItemDismissalGroup(int position) {
         checkIndex(position);
         return canBeDismissed() ? Collections.singleton(0) : Collections.<Integer>emptySet();
     }
 
     @Override
     public void dismissItem(int position, Callback<String> itemRemovedCallback) {
         checkIndex(position);
         dismiss(itemRemovedCallback);
     }
 
+    @Override
+    public final void visitItems(NodeVisitor visitor) {
+        if (mVisible) visitOptionalItem(visitor);
+    }
+
     /** @return Whether the optional item is currently visible. */
     public final boolean isVisible() {
         return mVisible;
     }
 
     /**
      * Notifies the parents in the tree about whether the visibility of this leaf changed. Call this
      * after a data change that could affect the return value of {@link #isVisible()}. The leaf is
      * initially considered hidden.
      */
@@ skipping 34 matching lines @@
     /**
      * Dismiss this item. The default implementation asserts, as by default items can't be
      * dismissed.
      * @param itemRemovedCallback Should be called with the title of the dismissed item, to announce
      * it for accessibility purposes.
      * @see TreeNode#dismissItem
      */
     protected void dismiss(Callback<String> itemRemovedCallback) {
         assert false;
     }
+
+    /**
+     * Visits this item. This method is called iff the optional item is currently visible.
+     * @param visitor The visitor with which to visit this item.
+     */
+    protected abstract void visitOptionalItem(NodeVisitor visitor);
 }