minor symfony#21354 [DependencyInjection] XML: optimize defaults parsing (dunglas)

This PR was merged into the 3.3-dev branch.

Discussion
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[DependencyInjection] XML: optimize defaults parsing

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

Defaults can be parsed only 1 time.

Commits
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dc115ab [DependencyInjection] XML: optimize defaults parsing

Author: fabpot

src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php

@@ -125,8 +125,9 @@ private function parseDefinitions(\DOMDocument $xml, $file)
             return;
         }
 
+        $defaults = $this->getServiceDefaults($xml, $file);
         foreach ($services as $service) {
-            if (null !== $definition = $this->parseDefinition($service, $file, $this->getServiceDefaults($xml, $file))) {
+            if (null !== $definition = $this->parseDefinition($service, $file, $defaults)) {
                 $this->container->setDefinition((string) $service->getAttribute('id'), $definition);
             }
         }