[Asset] Add support for preloading with links and HTTP/2 push

Author: dunglas

Resources/config/assets.xml

@@ -38,5 +38,13 @@
 
         <service id="assets.empty_version_strategy" class="Symfony\Component\Asset\VersionStrategy\EmptyVersionStrategy" public="false" />
 
+        <service id="assets.preload_manager" class="Symfony\Component\Asset\Preload\PreloadManager" public="false" />
+
+        <service id="asset.preload_listener" class="Symfony\Component\Asset\EventListener\PreloadListener">
+            <argument type="service" id="assets.preload_manager" />
+
+            <tag name="kernel.event_subscriber" />
+        </service>
+
     </services>
 </container>

Tests/DependencyInjection/FrameworkExtensionTest.php

@@ -375,6 +375,12 @@ public function testAssetsDefaultVersionStrategyAsService()
         $this->assertEquals('assets.custom_version_strategy', (string) $defaultPackage->getArgument(1));
     }
 
+    public function testAssetHasPreloadListener()
+    {
+        $container = $this->createContainerFromFile('assets');
+        $this->assertTrue($container->hasDefinition('asset.preload_listener'));
+    }
+
     public function testTranslator()
     {
         $container = $this->createContainerFromFile('full');

composer.json

@@ -60,6 +60,7 @@
     "conflict": {
         "phpdocumentor/reflection-docblock": "<3.0",
         "phpdocumentor/type-resolver": "<0.2.0",
+        "symfony/asset": "<3.3",
         "symfony/console": "<3.3"
     },
     "suggest": {