Merge branch '2.8' into 3.2

* 2.8:
  Fixes #22264 - add support for Chrome headless, see also Seldaek/monolog#966
  bumped Symfony version to 2.8.20
  updated VERSION for 2.8.19
  updated CHANGELOG for 2.8.19
  Dont call sprintf() when no placeholders are used

Author: fabpot

Definition.php

@@ -269,7 +269,7 @@ public function setMethodCalls(array $calls = array())
     public function addMethodCall($method, array $arguments = array())
     {
         if (empty($method)) {
-            throw new InvalidArgumentException(sprintf('Method name cannot be empty.'));
+            throw new InvalidArgumentException('Method name cannot be empty.');
         }
         $this->calls[] = array($method, $arguments);
 

Dumper/YamlDumper.php

@@ -93,7 +93,7 @@ private function addService($id, $definition)
         }
 
         if ($definition->isSynthetic()) {
-            $code .= sprintf("        synthetic: true\n");
+            $code .= "        synthetic: true\n";
         }
 
         if ($definition->isDeprecated()) {
@@ -113,7 +113,7 @@ private function addService($id, $definition)
         }
 
         if ($definition->isLazy()) {
-            $code .= sprintf("        lazy: true\n");
+            $code .= "        lazy: true\n";
         }
 
         if ($definition->getArguments()) {