Issue #1465584 by sun: Commit external library dependencies to Drupal core.

core/vendor/Symfony/Component/EventDispatcher/Event.php

...dor/Symfony/Component/EventDispatcher/EventDispatcher.php

...ny/Component/EventDispatcher/EventDispatcherInterface.php

...ny/Component/EventDispatcher/EventSubscriberInterface.php

core/vendor/Symfony/Component/EventDispatcher/LICENSE

core/vendor/Symfony/Component/EventDispatcher/README.md

core/vendor/Symfony/Component/EventDispatcher/composer.json

core/vendor/Symfony/Component/HttpKernel/Bundle/Bundle.php

...r/Symfony/Component/HttpKernel/Bundle/BundleInterface.php

...mponent/HttpKernel/CacheClearer/CacheClearerInterface.php

...y/Component/HttpKernel/CacheClearer/ChainCacheClearer.php

.../Symfony/Component/HttpKernel/CacheWarmer/CacheWarmer.php

...Component/HttpKernel/CacheWarmer/CacheWarmerAggregate.php

...Component/HttpKernel/CacheWarmer/CacheWarmerInterface.php

...ny/Component/HttpKernel/CacheWarmer/WarmableInterface.php

core/vendor/Symfony/Component/HttpKernel/Client.php

...endor/Symfony/Component/HttpKernel/Config/FileLocator.php

...ny/Component/HttpKernel/Controller/ControllerResolver.php

...ent/HttpKernel/Controller/ControllerResolverInterface.php

...omponent/HttpKernel/DataCollector/ConfigDataCollector.php