📰 Refactor SuggestionsSection change detection

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

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/OptionalLeaf.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/OptionalLeaf.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/OptionalLeaf.java
index 0a9cc68e7c16a3ca3cf242e4de53d0e4c0b4766d..af1836a7a1526cb5f1334739d769ba1a1e813d8d 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/OptionalLeaf.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/cards/OptionalLeaf.java
@@ -4,24 +4,32 @@
 
 package org.chromium.chrome.browser.ntp.cards;
 
+import android.support.annotation.CallSuper;
+
 import org.chromium.chrome.browser.ntp.snippets.SnippetArticle;
 
 /**
  * An optional leaf (i.e. single item) in the tree. Depending on its internal state (see
- * {@link #isShown()}), the item will be present or absent from the tree, by manipulating the values
- * returned from {@link ChildNode} methods. This allows the parent node to not have to add or remove
- * the optional leaf from its children manually.
+ * {@link #isVisible()}), the item will be present or absent from the tree, by manipulating the
+ * values returned from {@link ChildNode} methods. This allows the parent node to not have to add or
+ * remove the optional leaf from its children manually.
  *
  * For a non optional leaf, see {@link Leaf}. They have similar interfaces.
  */
 public abstract class OptionalLeaf extends ChildNode {
-    protected OptionalLeaf(NodeParent parent) {
+    private boolean mVisible;
+
+    /**
+     * Constructor for {@link OptionalLeaf}.
+     * By default it is not visible. See {@link #setVisible(boolean)} to update the visibility.
+     */
+    public OptionalLeaf(NodeParent parent) {
         super(parent);
     }
 
     @Override
     public int getItemCount() {
-        return isShown() ? 1 : 0;
+        return isVisible() ? 1 : 0;
     }
 
     @Override
@@ -48,6 +56,29 @@ public int getDismissSiblingPosDelta(int position) {
         return 0;
     }
 
+
+    /** @return Whether the optional item is currently visible. */
+    public final boolean isVisible() {
+        return mVisible;
+    }
+
+    /**
+     * Notifies the parents in the tree about whether the visibility of this leaf changed. Call this
+     * after a data change that could affect the return value of {@link #isVisible()}. The leaf is
+     * initially considered hidden.
+     */
+    @CallSuper
+    public void setVisible(boolean visible) {
+        if (mVisible == visible) return;
+        mVisible = visible;
+
+        if (visible) {
+            notifyItemInserted(0);
+        } else {
+            notifyItemRemoved(0);
+        }
+    }
+
     /**
      * Display the data for this item.
      * @param holder The view holder that should be updated.
@@ -63,9 +94,6 @@ public int getDismissSiblingPosDelta(int position) {
     @ItemViewType
     protected abstract int getItemViewType();
 
-    /** @return Whether the optional item is currently visible. */
-    public abstract boolean isShown();
-
     protected void checkIndex(int position) {
         if (position < 0 || position >= getItemCount()) {
             throw new IndexOutOfBoundsException(position + "/" + getItemCount());