Load all routes for local tasks via getRoutesByNames()

This seems like a reasonable performance optimization.

so, it looks like in the current implementation this would eliminate potentially several DB queries, at the cost of an extra foreach loop, which seems liek a reasonable tradeoff.

I might prefer a ternary instead of if/else here:

+    if ($route_names) {
+      $routes = $this->routeProvider->getRoutesByNames($route_names);
+    }
+    else {
+      $routes = array();
+    }

Looks good to me! Thanks @dawehner.

+++ b/core/lib/Drupal/Core/Menu/LocalTaskManager.phpundefined
@@ -192,11 +192,21 @@ public function getLocalTasksForRoute($route_name) {
+    // Fetch a bunch of routes at once.

Perhaps rather than the enjoyably flowery language of a "bunch of routes" we should change this to // Prefetch routes.

... if we need a comment at all :)

Back to RTBC

Committed 2f0e07f and pushed to 8.x. Thanks!