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

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

+// 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 android.support.annotation.IntDef;
+import android.support.v7.widget.RecyclerView.Adapter;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+/**
+ * View type values for the items that will be held by the NTP's RecyclerView.
+ *
+ * @see Adapter#getItemViewType(int)
+ */
+@IntDef({
+    ItemViewType.ABOVE_THE_FOLD,
+    ItemViewType.HEADER,
+    ItemViewType.SNIPPET,
+    ItemViewType.SPACING,
+    ItemViewType.STATUS,
+    ItemViewType.PROGRESS,
+    ItemViewType.ACTION,
+    ItemViewType.FOOTER,
+    ItemViewType.PROMO,
+    ItemViewType.ALL_DISMISSED
+})
+@Retention(RetentionPolicy.SOURCE)
+public @interface ItemViewType {
+
+    /**
+     * View type for the above the fold item
+     *
+     * @see Adapter#getItemViewType(int)
+     */
+    int ABOVE_THE_FOLD = 1;
+    /**
+     * View type for card group headers
+     *
+     * @see Adapter#getItemViewType(int)
+     */
+    int HEADER = 2;
+    /**
+     * View type for snippet cards
+     *
+     * @see Adapter#getItemViewType(int)
+     */
+    int SNIPPET = 3;
+    /**
+     * View type for a {@link SpacingItem} used to provide spacing at the end of the list.
+     *
+     * @see Adapter#getItemViewType(int)
+     */
+    int SPACING = 4;
+    /**
+     * View type for a {@link StatusItem}, the card displaying status information
+     *
+     * @see Adapter#getItemViewType(int)
+     */
+    int STATUS = 5;
+    /**
+     * View type for a {@link ProgressItem}, the progress indicator.
+     *
+     * @see Adapter#getItemViewType(int)
+     */
+    int PROGRESS = 6;
+    /**
+     * View type for a {@link ActionItem}, an action button.
+     *
+     * @see Adapter#getItemViewType(int)
+     */
+    int ACTION = 7;
+    /**
+     * View type for a {@link Footer}.
+     *
+     * @see Adapter#getItemViewType(int)
+     */
+    int FOOTER = 8;
+    /**
+     * View type for a {@link SignInPromo}.
+     *
+     * @see Adapter#getItemViewType(int)
+     */
+    int PROMO = 9;
+    /**
+     * View type for a {@link AllDismissedItem}.
+     *
+     * @see Adapter#getItemViewType(int)
+     */
+    int ALL_DISMISSED = 10;
+}