Add an experimental standalone content suggestions UI.

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

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NewTabPageAdapter.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NewTabPageAdapter.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NewTabPageAdapter.java
index 4d748070fe131c247518b1021d03560dd0d965fb..97c1461188237e05c96cf59cdacbb3bbb9160be1 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NewTabPageAdapter.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/NewTabPageAdapter.java
@@ -4,6 +4,7 @@
 
 package org.chromium.chrome.browser.ntp.cards;
 
+import android.support.annotation.Nullable;
 import android.support.v7.widget.RecyclerView;
 import android.support.v7.widget.RecyclerView.Adapter;
 import android.support.v7.widget.RecyclerView.ViewHolder;
@@ -27,13 +28,15 @@ import org.chromium.chrome.browser.offlinepages.OfflinePageBridge;
  */
 public class NewTabPageAdapter extends Adapter<NewTabPageViewHolder> implements NodeParent {
     private final NewTabPageManager mNewTabPageManager;
+    @Nullable
     private final View mAboveTheFoldView;
     private final UiConfig mUiConfig;
     private NewTabPageRecyclerView mRecyclerView;
 
     private final InnerNode mRoot;
 
-    private final AboveTheFoldItem mAboveTheFold = new AboveTheFoldItem();
+    @Nullable
+    private final AboveTheFoldItem mAboveTheFold;
     private final SectionList mSections;
     private final SignInPromo mSigninPromo;
     private final AllDismissedItem mAllDismissed;
@@ -45,14 +48,14 @@ public class NewTabPageAdapter extends Adapter<NewTabPageViewHolder> implements
      *
      * @param manager the NewTabPageManager to use to interact with the rest of the system.
      * @param aboveTheFoldView the layout encapsulating all the above-the-fold elements
-     *                         (logo, search box, most visited tiles)
+     *         (logo, search box, most visited tiles), or null if only suggestions should
+     *         be displayed.
      * @param uiConfig the NTP UI configuration, to be passed to created views.
      * @param offlinePageBridge the OfflinePageBridge used to determine if articles are available
-     *                              offline.
-     *
+     *         offline.
      */
-    public NewTabPageAdapter(NewTabPageManager manager, View aboveTheFoldView, UiConfig uiConfig,
-            OfflinePageBridge offlinePageBridge) {
+    public NewTabPageAdapter(NewTabPageManager manager, @Nullable View aboveTheFoldView,
+            UiConfig uiConfig, OfflinePageBridge offlinePageBridge) {
         mNewTabPageManager = manager;
         mAboveTheFoldView = aboveTheFoldView;
         mUiConfig = uiConfig;
@@ -63,8 +66,13 @@ public class NewTabPageAdapter extends Adapter<NewTabPageViewHolder> implements
         mAllDismissed = new AllDismissedItem();
         mFooter = new Footer();
 
-        mRoot.addChildren(
-                mAboveTheFold, mSections, mSigninPromo, mAllDismissed, mFooter, mBottomSpacer);
+        if (mAboveTheFoldView == null) {

[Michael van Ouwerkerk, 2017/01/04 16:45:35]

I worry this will lead to many unhandled edge cases, that view being always
present is such a central assumption.

[Bernhard Bauer, 2017/01/05 12:02:15]

Hm, if it is, that assumption is going to be wrong :) And in that case I'd
rather learn about it via a NullPointerException.

(Also, because the above-the-fold view already may or may not be attached to the
RecyclerView, I think in practice the majority of cases already deal with a
potentially missing above-the-fold view)

[Michael van Ouwerkerk, 2017/01/05 13:58:34]

I think it may also fail in ways that are not NullPointerExceptions. But, maybe
it's not that bad for the reasons you gave.

+            mAboveTheFold = null;
+        } else {
+            mAboveTheFold = new AboveTheFoldItem();
+            mRoot.addChild(mAboveTheFold);
+        }
+        mRoot.addChildren(mSections, mSigninPromo, mAllDismissed, mFooter, mBottomSpacer);

[dgn, 2017/01/04 12:19:43]

Is the bottom spacer still necessary? IIRC that was there only because we needed
to push content up enough to have the above/below-the-fold split.

[Bernhard Bauer, 2017/01/05 12:02:15]

Done. We need to add some checks to allow the adapter to handle the case when
the SPACING item is now missing, but the view code is already handling it
anyway.

 
         updateAllDismissedVisibility();
         mRoot.setParent(this);
@@ -127,6 +135,8 @@ public class NewTabPageAdapter extends Adapter<NewTabPageViewHolder> implements
     }
 
     public int getAboveTheFoldPosition() {
+        if (mAboveTheFoldView == null) return RecyclerView.NO_POSITION;
+
         return getChildPositionOffset(mAboveTheFold);
     }