Unify NewTabPageItem and ItemGroup into a single tree-structured interface.

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

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SingleItemGroup.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SingleItemGroup.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SingleItemGroup.java
deleted file mode 100644
index 3d8a9ca9443c9132f9be98c6ac87d32e1be700e2..0000000000000000000000000000000000000000
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/SingleItemGroup.java
+++ /dev/null
@@ -1,21 +0,0 @@
-// Copyright 2016 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 java.util.Collections;
-import java.util.List;
-
-/**
- * A single item that represents itself as a group.
- */
-public abstract class SingleItemGroup implements ItemGroup, NewTabPageItem {
-    private final List<NewTabPageItem> mItems =
-            Collections.<NewTabPageItem>singletonList(this);
-
-    @Override
-    public List<NewTabPageItem> getItems() {
-        return mItems;
-    }
-}