Add new NTP layout with snippet cards and hide it behind a flag

chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageCardsManager.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageCardsManager.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageCardsManager.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageCardsManager.java
new file mode 100644
index 0000000000000000000000000000000000000000..9f3d1bce690e311d3d39cf8398a8aae0c6a36bf5
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageCardsManager.java
@@ -0,0 +1,77 @@
+// 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;
+
+import org.chromium.chrome.browser.ntp.snippets.NewTabPageAdapter;
+import org.chromium.chrome.browser.ntp.snippets.SnippetsManager;
+
+import java.util.List;
+import java.util.Observable;
+import java.util.Observer;
+
+/**
+ * A class that handles merging above the fold elements and below the fold cards.
+ */
+public class NewTabPageCardsManager implements Observer {

[newt (away), 2016/03/23 05:29:38]

I'm not convinced this class should exist. Could everything here simply be
merged into NewTabPageAdapter? The constants and interface defined in this class
are core pieces of NewTabPageAdapter, so it makes sense to me to move them into
NewTabPageAdapter.

[May, 2016/03/23 19:22:56]

Yeah, I think NewTabPageAdapter could be combined with this. WRT your later
comments about NewTabPageCardsManager / NewTabPageAdapter / SnippetsManager
having blurry purposes, the intention is is for NewTabPageCardsManager (and
combined NewTabPageAdapter I suppose) to handle and merge all the cards that we
will show on the NTP. There's cards other than snippets that are planned in the
pipeline (but all still in the PRD stage).

+    /**
+     * Describes the above the fold item
+     */
+    public static final int SNIPPET_ITEM_ABOVE_THE_FOLD = 1;
+    /**
+     * Describes the header of a group of similar card snippets
+     */
+    public static final int SNIPPET_ITEM_TYPE_HEADER = 2;
+    /**
+     * Describes a single card snippet
+     */
+    public static final int SNIPPET_ITEM_TYPE_SNIPPET = 3;
+
+    /** Base type for anything to add to the new tab page

[newt (away), 2016/03/23 05:29:38]

fix wrapping, spacing, and indentation in comments throughout this file

[May, 2016/03/23 19:22:56]

Done.

+    */
+    public interface NewTabPageListItem {
+        /**
+         * Returns the type of this snippet item (SNIPPET_ITEM_TYPE_HEADER or
+         * SNIPPET_ITEM_TYPE_SNIPPET). This is so we can distinguish between different elements
+         * that are held in a single RecyclerView holder.
+         *
+        * @return the type of this list item.
+        */
+        public int getType();
+    }
+
+    /** Represents the data for a header of a group of snippets

[newt (away), 2016/03/23 05:29:38]

This comment doesn't seem right

[May, 2016/03/23 19:22:56]

Done.

+     */
+    public static class AboveTheFoldListItem implements NewTabPageListItem {
+        public AboveTheFoldListItem() {}
+
+        @Override
+        public int getType() {
+            return NewTabPageCardsManager.SNIPPET_ITEM_ABOVE_THE_FOLD;
+        }
+    }
+
+    private SnippetsManager mSnippetsManager;
+    private NewTabPageAdapter mDataAdapter;
+    private NewTabPageLayout mAboveTheFoldContentsView;
+
+    public NewTabPageCardsManager(SnippetsManager manager, NewTabRecyclerView recyclerView,

[newt (away), 2016/03/23 05:29:38]

javadoc

[May, 2016/03/23 19:22:56]

Done.

+            NewTabPageLayout aboveTheFoldView) {
+        mSnippetsManager = manager;
+        mAboveTheFoldContentsView = aboveTheFoldView;
+        mDataAdapter = new NewTabPageAdapter(mSnippetsManager, mAboveTheFoldContentsView);
+        mDataAdapter.setAboveTheFoldItem(new AboveTheFoldListItem());
+        recyclerView.setAdapter(mDataAdapter);
+        mSnippetsManager.addObserver(this);
+    }
+
+    @Override
+    @SuppressWarnings("unchecked")
+    public void update(Observable observable, Object data) {
+        if (data instanceof List) {

[newt (away), 2016/03/23 05:29:37]

And if this instanceof check fails? Seems like a serious programming error (and
one that we'd want to find out about). I'd remove the instanceof check and just
use a cast here. Otherwise, a silent error might creep in where snippets aren't
being updated and no one notices for several releases.

Actually, see my comment later above removing use of Observer/Observable
altogether. This is just another reason to do so.

[May, 2016/03/23 19:22:56]

Yeah, I was trying to avoid defining yet another new interface when there's
already nice support for it, but I'll remove it. It's more complex than what we
need anyway.

+            List<NewTabPageListItem> snippets = (List<NewTabPageListItem>) data;
+            mDataAdapter.setSnippetListItems(snippets);
+        }
+    }
+}