bug symfony#26393 [DI] Skip resource tracking if disabled (chalasr)

This PR was merged into the 3.4 branch.

Discussion
----------

 [DI] Skip resource tracking if disabled

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | symfony#26388
| License       | MIT
| Doc PR        | n/a

Commits
-------

0b748fa [DI] Skip resource tracking if disabled

Author: fabpot

src/Symfony/Component/DependencyInjection/ContainerBuilder.php

@@ -346,9 +346,11 @@ public function getReflectionClass($class, $throw = true)
         try {
             if (isset($this->classReflectors[$class])) {
                 $classReflector = $this->classReflectors[$class];
-            } else {
+            } elseif ($this->trackResources) {
                 $resource = new ClassExistenceResource($class, false);
                 $classReflector = $resource->isFresh(0) ? false : new \ReflectionClass($class);
+            } else {
+                $classReflector = new \ReflectionClass($class);
             }
         } catch (\ReflectionException $e) {
             if ($throw) {