[HttpKernel][FrameworkBundle] fix compat with Debug component

Author: nicolas-grekas

FrameworkBundle.php

@@ -35,6 +35,7 @@
 use Symfony\Component\Cache\DependencyInjection\CachePoolPrunerPass;
 use Symfony\Component\Config\Resource\ClassExistenceResource;
 use Symfony\Component\Console\DependencyInjection\AddConsoleCommandPass;
+use Symfony\Component\Debug\ErrorHandler as LegacyErrorHandler;
 use Symfony\Component\DependencyInjection\Compiler\PassConfig;
 use Symfony\Component\DependencyInjection\Compiler\RegisterReverseContainerPass;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
@@ -89,6 +90,9 @@ class FrameworkBundle extends Bundle
     public function boot()
     {
         ErrorHandler::register(null, false)->throwAt($this->container->getParameter('debug.error_handler.throw_at'), true);
+        if (class_exists(LegacyErrorHandler::class, false)) {
+            LegacyErrorHandler::register(null, false)->throwAt($this->container->getParameter('debug.error_handler.throw_at'), true);
+        }
 
         if ($this->container->getParameter('kernel.http_method_override')) {
             Request::enableHttpMethodParameterOverride();