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

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

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NodeVisitor.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NodeVisitor.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NodeVisitor.java
new file mode 100644
index 0000000000000000000000000000000000000000..1e094e20d2175eba56946cab173291035e1bbdaf
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NodeVisitor.java
@@ -0,0 +1,70 @@
+// Copyright 2017 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 org.chromium.chrome.browser.ntp.snippets.SnippetArticle;
+import org.chromium.chrome.browser.suggestions.ContentSuggestionsAdditionalAction;
+
+/**
+ * Allows implementing a visitor pattern to iterate over all items under a (sub-)tree.
+ */
+public interface NodeVisitor {
+    /**
+     * Visits the above-the-fold item.
+     */
+    void visitAboveTheFoldItem();
+
+    /**
+     * Visits an action item.
+     * @param currentAction The action enum value for the item.
+     */
+    void visitActionItem(@ContentSuggestionsAdditionalAction int currentAction);
+
+    /**
+     * Visits the "all dimissed" item.
+     */
+    void visitAllDismissedItem();
+
+    /**
+     * Visits the footer.
+     */
+    void visitFooter();
+
+    /**
+     * Visits a progress item.
+     */
+    void visitProgressItem();
+
+    /**
+     * Visits a sign-in promo.
+     */
+    void visitSignInPromo();
+
+    /**
+     * Visits a spacing item.
+     */
+    void visitSpacingItem();
+
+    /**
+     * Visits a "no suggestions" item.
+     */
+    void visitNoSuggestionsItem();
+
+    /**
+     * Visits a suggestion.
+     * @param suggestion The {@link SnippetArticle} represented by the item.
+     */
+    void visitSuggestion(SnippetArticle suggestion);
+
+    /**
+     * Visits a header.
+     */
+    void visitHeader();
+
+    /**
+     * Visits the tile grid.
+     */
+    void visitTileGrid();
+}