[Android NTP] Move dismissing items 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 0c57425be4eae349cdee5aaf94c3c5987a1a61da..f54db9da5637255947a33701d2119168626456af 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
@@ -4,6 +4,7 @@
 
 package org.chromium.chrome.browser.ntp.cards;
 
+import org.chromium.base.Callback;
 import org.chromium.base.VisibleForTesting;
 import org.chromium.chrome.browser.ntp.snippets.SnippetArticle;
 
@@ -17,16 +18,16 @@ public class InnerNode extends ChildNode implements NodeParent {
     private final List<TreeNode> mChildren = new ArrayList<>();
 
     private int getChildIndexForPosition(int position) {
-        if (position < 0) {
-            throw new IndexOutOfBoundsException(Integer.toString(position));
-        }
+        checkIndex(position);
         int numItems = 0;
         int numChildren = mChildren.size();
         for (int i = 0; i < numChildren; i++) {
             numItems += mChildren.get(i).getItemCount();
             if (position < numItems) return i;
         }
-        throw new IndexOutOfBoundsException(position + "/" + numItems);
+        // checkIndex() will have caught this case already.
+        assert false;
+        return -1;
     }
 
     private int getStartingOffsetForChildIndex(int childIndex) {
@@ -84,6 +85,13 @@ public class InnerNode extends ChildNode implements NodeParent {
     }
 
     @Override
+    public void dismissItem(int position, Callback<String> itemRemovedCallback) {
+        int index = getChildIndexForPosition(position);
+        getChildren().get(index).dismissItem(
+                position - getStartingOffsetForChildIndex(index), itemRemovedCallback);
+    }
+
+    @Override
     public int getDismissSiblingPosDelta(int position) {
         int index = getChildIndexForPosition(position);
         return mChildren.get(index).getDismissSiblingPosDelta(