Fix crash on tablet when reordering bookmark page is closed by notification

If reordering bookmark page is closed by clicking 'Close Incognito Tabs' on
notifications, then the runnable posted by recyclerView will be run. But at
that moment, bookmark model has been assigned to null. This CL makes it
only run when view is being attached to window.

Bug: 1017073
Change-Id: I328550a11432a7288b9508227f9634e9719ae357
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1884350Reviewed-by: Theresa  <twellington@chromium.org>
Commit-Queue: Lijin Shen <lazzzis@google.com>
Cr-Commit-Position: refs/heads/master@{#710016}

chrome/browser/ui/android/widget/java/src/org/chromium/chrome/browser/ui/widget/dragreorder/DragReorderableListAdapter.java

@@ -92,7 +92,9 @@ public abstract class DragReorderableListAdapter<T> extends RecyclerView.Adapter
         @Override
         public void clearView(RecyclerView recyclerView, ViewHolder viewHolder) {
             super.clearView(recyclerView, viewHolder);
-            if (viewHolder.getAdapterPosition() != mStart) {
+            // no need to commit change if recycler view is not attached to window, e.g.:
+            // dragging is terminated by destroying activity
+            if (viewHolder.getAdapterPosition() != mStart && recyclerView.isAttachedToWindow()) {
                 // Commit the position change for the dragged item when it's dropped and
                 // recyclerView has finished layout computing
                 recyclerView.post(() -> setOrder(mElements));