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

chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SectionHeader.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.snippets;
 
 import org.chromium.chrome.browser.ntp.cards.ItemViewType;
 import org.chromium.chrome.browser.ntp.cards.NewTabPageViewHolder;
+import org.chromium.chrome.browser.ntp.cards.NodeVisitor;
 import org.chromium.chrome.browser.ntp.cards.OptionalLeaf;
 
 /**
- * Represents the data for a header of a group of snippets
+ * Represents the data for a header of a group of snippets.
  */
 public class SectionHeader extends OptionalLeaf {
     /** The header text to be shown. */
     private final String mHeaderText;
 
     public SectionHeader(String headerText) {
         this.mHeaderText = headerText;
         setVisible(true);
     }
 
     @Override
     @ItemViewType
     public int getItemViewType() {
         return ItemViewType.HEADER;
     }
 
     public String getHeaderText() {
         return mHeaderText;
     }
 
     @Override
     protected void onBindViewHolder(NewTabPageViewHolder holder) {
         assert holder instanceof SectionHeaderViewHolder;
         ((SectionHeaderViewHolder) holder).onBindViewHolder(this);
     }
-}
+
+    @Override
+    public void visitOptionalItem(NodeVisitor visitor) {
+        visitor.visitHeader();
+    }
+}