[Android NTP] Move more of the dismissal logic into the tree.

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 9dd7967cfd014b9710b601d19ec961214fdd3ce0..fcb153e1775541d10ef41188d310666923ce0642 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
@@ -9,7 +9,10 @@ import org.chromium.base.VisibleForTesting;
 import org.chromium.chrome.browser.ntp.snippets.SnippetArticle;
 
 import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
+import java.util.Set;
 
 /**
  * An inner node in the tree: the root of a subtree, with a list of child nodes.
@@ -85,17 +88,19 @@ public class InnerNode extends ChildNode implements NodeParent {
     }
 
     @Override
-    public void dismissItem(int position, Callback<String> itemRemovedCallback) {
+    public Set<Integer> getItemDismissalGroup(int position) {
         int index = getChildIndexForPosition(position);
-        getChildren().get(index).dismissItem(
-                position - getStartingOffsetForChildIndex(index), itemRemovedCallback);
+        int offset = getStartingOffsetForChildIndex(index);
+        Set<Integer> itemDismissalGroup =
+                getChildren().get(index).getItemDismissalGroup(position - offset);
+        return offsetBy(itemDismissalGroup, offset);
     }
 
     @Override
-    public int getDismissSiblingPosDelta(int position) {
+    public void dismissItem(int position, Callback<String> itemRemovedCallback) {
         int index = getChildIndexForPosition(position);
-        return mChildren.get(index).getDismissSiblingPosDelta(
-                position - getStartingOffsetForChildIndex(index));
+        getChildren().get(index).dismissItem(
+                position - getStartingOffsetForChildIndex(index), itemRemovedCallback);
     }
 
     @Override
@@ -172,4 +177,24 @@ public class InnerNode extends ChildNode implements NodeParent {
     final List<TreeNode> getChildren() {
         return mChildren;
     }
+
+    /**
+     * Helper method that adds an offset value to a set of integers.
+     * @param set a set of integers
+     * @param offset the offset to add to the set.
+     * @return a set of integers with the {@code offset} value added to the input {@code set}.
+     */
+    private static Set<Integer> offsetBy(Set<Integer> set, int offset) {
+        // Optimizations for empty and singleton sets:
+        if (set.isEmpty()) return Collections.emptySet();
+        if (set.size() == 1) {
+            return Collections.singleton(set.iterator().next() + offset);
+        }
+
+        Set<Integer> offsetSet = new HashSet<>();
+        for (int value : set) {
+            offsetSet.add(value + offset);
+        }
+        return offsetSet;
+    }
 }