Views preview not working for REST display

After applying the patch from #2416971: Remove Url::__toString():

Uncaught PHP Exception Symfony\Component\Routing\Exception\RouteNotFoundException: "Route "views.testrest.rest_export_1" does not exist." at /var/www/html/d8.local/drupal/core/lib/Drupal/Core/Routing/RouteProvider.php line 145

Something like this fixes that, no idea if this is going to break something else. Let's see what the testbot says.

+++ b/core/modules/views/src/Plugin/views/display/PathPluginBase.php
@@ -309,7 +307,7 @@ public function getMenuLinks() {
-          'route_name' => isset($view_route_names[$view_id_display]) ? $view_route_names[$view_id_display] : "view.$view_id_display",
+          'route_name' => $this->getRouteName(),

@@ -490,11 +488,28 @@ public function validate() {
+  /**
+   * {@inheritdoc}
+   */
+  public function getRouteName() {
+    $view_id = $this->view->storage->id();
+    $display_id = $this->display['id'];
+    $view_route_key = "$view_id.$display_id";
+
+    // Check for overridden route names.
+    $view_route_names = $this->getAlteredRouteNames();
+
+    return (isset($view_route_names[$view_route_key]) ? $view_route_names[$view_route_key] : "views.$view_route_key");
+  }
+

Ah, seems like a mistake in the committed patch in #2409209: Replace all _url() calls beside the one in _l(). So this is the right way to fix it.
I guess this will definitely need test coverage since this broke once and it might break again. I'll try to pick that up together with #2396253: Respect format configuration on REST views display

First time writing one of those. Is something like this ok?

Followup created #2450055: Add constant for prefix for views dynamic routes