[Android NTP] Move getDismissSiblingPosDelta into the TreeNode interface.

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

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/TreeNode.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/TreeNode.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/TreeNode.java
index d05487539a4c70aeeb12166b5b5bdfb2ec5399f7..6c76fcb6c7be149c5e4e62f37022bf1ae8c3c68e 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/TreeNode.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/TreeNode.java
@@ -38,4 +38,16 @@ interface TreeNode {
      * an article.
      */
     SnippetArticle getSuggestionAt(int position);
+
+    /**
+     * The dismiss sibling is an item that should be dismissed at the same time as the provided
+     * one. For example, if we want to dismiss a status card that has a More button attached, the
+     * button is the card's dismiss sibling. This function returns the adapter position delta to
+     * apply to get to the sibling from the provided item. For the previous example, it would return
+     * {@code +1}, as the button comes right after the status card.
+     *
+     * @return a position delta to apply to the position of the provided item to get the adapter
+     * position of the item to animate. Returns {@code 0} if there is no dismiss sibling.
+     */
+    int getDismissSiblingPosDelta(int position);
 }