Fix always-null children on NotificationEntry

Looks like _someone_ decided to make an array of children and _never_
poplate it.

What used to happen was that callers into NotificationEntry would grab
the row and call ExpandableNotificationRow#getNotificationChildren() on
it to iterate the children and call things (notably setKeepInParent()).
During the work to refactor NotficationEntry into its own class,
NotificationEntry#getChildren() was created so that we could iterate the
entry's children instead of the view's children. Unfortunately it was
never populated.

For now, just call through to
ExpandableNotificationRow#getNotificationChildren() and map those to
their entries.

Fixes: 130018576
Test: atest SystemUITests; visual
Change-Id: Ica629b96c8fa2ee2fb45fdf588ee7d1efc836883

packages/SystemUI/src/com/android/systemui/statusbar/notification/NotificationEntryManager.java

@@ -355,10 +355,10 @@ public class NotificationEntryManager implements
                     // a child we're keeping around for reply!
                     continue;
                 }
-                entry.setKeepInParent(true);
+                childEntry.setKeepInParent(true);
                 // we need to set this state earlier as otherwise we might generate some weird
                 // animations
-                entry.removeRow();
+                childEntry.removeRow();
             }
         }
     }

packages/SystemUI/src/com/android/systemui/statusbar/notification/collection/NotificationEntry.java

@@ -122,7 +122,6 @@ public final class NotificationEntry {
     public boolean suspended;
 
     private NotificationEntry parent; // our parent (if we're in a group)
-    private ArrayList<NotificationEntry> children = new ArrayList<NotificationEntry>();
     private ExpandableNotificationRow row; // the outer expanded view
 
     private int mCachedContrastColor = COLOR_INVALID;
@@ -277,10 +276,20 @@ public final class NotificationEntry {
 
     @Nullable
     public List<NotificationEntry> getChildren() {
-        if (children.size() <= 0) {
+        if (row == null) {
             return null;
         }
 
+        List<ExpandableNotificationRow> rowChildren = row.getNotificationChildren();
+        if (rowChildren == null) {
+            return null;
+        }
+
+        ArrayList<NotificationEntry> children = new ArrayList<>();
+        for (ExpandableNotificationRow child : rowChildren) {
+            children.add(child.getEntry());
+        }
+
         return children;
     }
 
@@ -740,7 +749,9 @@ public final class NotificationEntry {
         if (notification == null || !notification.isClearable()) {
             return false;
         }
-        if (children.size() > 0) {
+
+        List<NotificationEntry> children = getChildren();
+        if (children != null && children.size() > 0) {
             for (int i = 0; i < children.size(); i++) {
                 NotificationEntry child =  children.get(i);
                 if (!child.isClearable()) {