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

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

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/OptionalLeaf.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/OptionalLeaf.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/OptionalLeaf.java
index 7bda849695ebe655abc73973361dec34264e00d6..19af66a7e1d450439f28075e4181d70d359ff0c7 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/OptionalLeaf.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/OptionalLeaf.java
@@ -7,7 +7,6 @@ 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;
@@ -41,12 +40,6 @@ public abstract class OptionalLeaf extends ChildNode {
     }
 
     @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();
@@ -58,6 +51,11 @@ public abstract class OptionalLeaf extends ChildNode {
         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;
@@ -112,4 +110,10 @@ public abstract class OptionalLeaf extends ChildNode {
     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);
 }