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..65f90ea4a154c58dd70ec27fd299d1a8fafc5bb6
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/NewTabPageCardsManager.java
@@ -0,0 +1,150 @@
+// 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 android.support.v7.widget.RecyclerView.Adapter;
+import android.view.ViewGroup;
+
+import org.chromium.chrome.browser.ntp.snippets.SnippetCardViewHolder;
+import org.chromium.chrome.browser.ntp.snippets.SnippetHeaderViewHolder;
+import org.chromium.chrome.browser.ntp.snippets.SnippetsManager;
+import org.chromium.chrome.browser.ntp.snippets.SnippetsManager.SnippetsManagerObserver;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * A class that handles merging above the fold elements and below the fold cards into an adapter
+ * that will be used to back the NTP RecyclerView. The first element in the adapter should always be
+ * the above-the-fold view (containing the logo, search box, and most visited tiles) and subsequent
+ * elements will be the cards shown to the user
+ */
+public class NewTabPageCardsManager extends Adapter<NewTabPageViewHolder>

[newt (away), 2016/03/24 19:47:38]

I think NewTabPageAdapter is a better name here. The presentation as cards is
secondary, and, in fact, some of the elements in this adapter (such as the logo,
fakebox, most visited sites, and the article headers) aren't cards at all.

[dgn, 2016/03/28 21:33:02]

Done.

+        implements SnippetsManagerObserver {
+    /**
+     * Describes the above the fold item

[newt (away), 2016/03/24 19:47:38]

This comment is rather vague. Could you make it more useful? In particular, it'd
be helpful to mention that these values are "view types" returned by
ecyclerView.Adapter.getItemViewType().

[dgn, 2016/03/28 21:33:02]

Done.

+     */
+    public static final int SNIPPET_ITEM_ABOVE_THE_FOLD = 1;

[newt (away), 2016/03/24 19:47:38]

can these type constants be private?

[dgn, 2016/03/28 21:33:02]

It needs to be used at least by NewTabPageListItem's subclasses. I could make it
protected in there, maybe? I don't think it changes much at that point though.
I'll revisit after the SnippetsManager refactoring.

+    /**
+     * 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
+     */
+    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 an item in the RecyclerView that will hold the above the fold contents for the
+     * NTP
+     */
+    static class AboveTheFoldListItem implements NewTabPageListItem {

[newt (away), 2016/03/24 19:47:38]

make this class and the class below private, if possible

[dgn, 2016/03/28 21:33:02]

Done.

+        public AboveTheFoldListItem() {}
+
+        @Override
+        public int getType() {
+            return NewTabPageCardsManager.SNIPPET_ITEM_ABOVE_THE_FOLD;
+        }
+    }
+
+    static class NewTabPageAboveTheFoldViewHolder extends NewTabPageViewHolder {

[newt (away), 2016/03/24 19:47:38]

this name should parallel the class name above.

[dgn, 2016/03/28 21:33:02]

Done.

+        public NewTabPageAboveTheFoldViewHolder(NewTabPageLayout view, SnippetsManager manager) {
+            super(view, manager);
+        }
+
+        @Override
+        public void onBindViewHolder(NewTabPageListItem snippetItem) {
+            // nothing to do
+        }
+    }
+
+    private final NewTabPageLayout mNewTabPageLayout;
+    private final AboveTheFoldListItem mNewTabPageAboveTheFoldItem;
+    private final SnippetsManager mSnippetsManager;
+    private List<NewTabPageListItem> mNewTabPageListItems;

[newt (away), 2016/03/24 19:47:38]

might as well make this final too

[dgn, 2016/03/28 21:33:02]

Done.

+
+    /**
+     * Constructor to create the manager for all the cards to display on the NTP
+     *
+     * @param snippetsManager the SnippetsManager to use
+     * @param newTabPageLayout the layout encapsulating all the above-the-fold elements
+     * (logo, search box, most visited tiles)
+     */
+    public NewTabPageCardsManager(
+            SnippetsManager snippetsManager, NewTabPageLayout newTabPageLayout) {
+        mNewTabPageLayout = newTabPageLayout;
+        mSnippetsManager = snippetsManager;
+        mNewTabPageAboveTheFoldItem = new AboveTheFoldListItem();

[newt (away), 2016/03/24 19:47:38]

Likewise, this member variable name should match the class name
(AboveTheFoldListItem). In general, avoid creating multiple different
terminologies for the same item unless there's a good reason for it.

[dgn, 2016/03/28 21:33:02]

Done.

+        mNewTabPageListItems = new ArrayList<NewTabPageListItem>();
+        mNewTabPageListItems.add(mNewTabPageAboveTheFoldItem);
+
+        mSnippetsManager.setObserver(this);
+    }
+
+    @Override
+    public void onSnippetsReceived(List<NewTabPageListItem> listSnippets) {
+        setSnippetListItems(listSnippets);
+    }
+
+    /**
+     * Sets the list of items to display in the snippets RecyclerView
+     *
+     * @param listItems the new list of items to display
+     */
+    public void setSnippetListItems(List<NewTabPageListItem> listItems) {
+        mNewTabPageListItems.clear();
+        mNewTabPageListItems.add(mNewTabPageAboveTheFoldItem);
+        mNewTabPageListItems.addAll(listItems);
+        notifyDataSetChanged();
+    }
+
+    @Override
+    public int getItemViewType(int position) {
+        return mNewTabPageListItems.get(position).getType();
+    }
+
+    @Override
+    public NewTabPageViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
+        if (viewType == NewTabPageCardsManager.SNIPPET_ITEM_ABOVE_THE_FOLD) {
+            return new NewTabPageAboveTheFoldViewHolder(mNewTabPageLayout, mSnippetsManager);
+        }
+
+        if (viewType == NewTabPageCardsManager.SNIPPET_ITEM_TYPE_HEADER) {
+            return new SnippetHeaderViewHolder(
+                    SnippetHeaderViewHolder.createView(parent), mSnippetsManager);
+        }
+
+        if (viewType == NewTabPageCardsManager.SNIPPET_ITEM_TYPE_SNIPPET) {
+            return new SnippetCardViewHolder(
+                    SnippetCardViewHolder.createView(parent), mSnippetsManager);
+        }
+
+        return null;
+    }
+
+    @Override
+    public void onBindViewHolder(NewTabPageViewHolder holder, final int position) {
+        holder.onBindViewHolder(mNewTabPageListItems.get(position));
+    }
+
+    @Override
+    public int getItemCount() {
+        return mNewTabPageListItems.size();
+    }
+}