[Android NTP] Move getDismissSiblingPosDelta into the TreeNode interface.

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

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/InnerNode.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/InnerNode.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/InnerNode.java
index 8c0078ae9007e8e6ce91dd69738dc4b2dede56a6..4e95cbfbf9ee584ca301cc320bdaf5b155ef1f2d 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/InnerNode.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/InnerNode.java
@@ -18,7 +18,7 @@ public abstract class InnerNode extends ChildNode implements NodeParent {
 
     protected abstract List<TreeNode> getChildren();
 
-    int getChildIndexForPosition(int position) {
+    private int getChildIndexForPosition(int position) {
         List<TreeNode> children = getChildren();
         int numItems = 0;
         int numChildren = children.size();
@@ -42,6 +42,13 @@ public abstract class InnerNode extends ChildNode implements NodeParent {
         return getStartingOffsetForChildIndex(getChildren().indexOf(child));
     }
 
+    /**
+     * Returns the child whose subtree contains the item at the given position.
+     */
+    TreeNode getChildForPosition(int position) {
+        return getChildren().get(getChildIndexForPosition(position));
+    }
+
     @Override
     public int getItemCount() {
         int numItems = 0;
@@ -74,6 +81,13 @@ public abstract class InnerNode extends ChildNode implements NodeParent {
     }
 
     @Override
+    public int getDismissSiblingPosDelta(int position) {
+        int index = getChildIndexForPosition(position);
+        return getChildren().get(index).getDismissSiblingPosDelta(
+                position - getStartingOffsetForChildIndex(index));
+    }
+
+    @Override
     public void onItemRangeChanged(TreeNode child, int index, int count) {
         notifyItemRangeChanged(getStartingOffsetForChild(child) + index, count);
     }