Fix crash on fast consecutive item moves in the Windows app list.

ui/app_list/views/apps_grid_view.cc

Index: ui/app_list/views/apps_grid_view.cc
diff --git a/ui/app_list/views/apps_grid_view.cc b/ui/app_list/views/apps_grid_view.cc
index 25334137e67f26e44d3420c8ff82a26f42b60507..35eb6f40ed20eaeae9efa451866beac67c9c9979 100644
--- a/ui/app_list/views/apps_grid_view.cc
+++ b/ui/app_list/views/apps_grid_view.cc
@@ -557,6 +557,11 @@ void AppsGridView::UpdateDrag(Pointer pointer, const gfx::Point& point) {
     // Move the view to the front so that it appears on top of other views.
     ReorderChildView(drag_view_, -1);
     bounds_animator_.StopAnimatingView(drag_view_);
+    // Stopping the animation may have invalidated our drag view due to the
+    // view hierarchy changing.
+    if (!drag_view_)
+      return;
+
     StartSettingUpSynchronousDrag();
     if (!dragging_for_reparent_item_)
       StartDragAndDropHostDrag(point);