minor #27975 [MonologBridge] Improve FirePHPHandler (dunglas)

This PR was merged into the 2.8 branch.

Discussion
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[MonologBridge] Improve FirePHPHandler

| Q             | A
| ------------- | ---
| Branch?       | 2.8
| Bug fix?      | no
| New feature?  | no <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets |n/a
| License       | MIT
| Doc PR        | n/a

Fix a call to a parent static property. Remove a useless call to `getRequest()`

Commits
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1d93b5e [MonologBridge] Improve FirePHPHandler

src/Symfony/Bridge/Monolog/Handler/FirePHPHandler.php

@@ -38,9 +38,10 @@ public function onKernelResponse(FilterResponseEvent $event)
             return;
         }
 
-        if (!preg_match('{\bFirePHP/\d+\.\d+\b}', $event->getRequest()->headers->get('User-Agent'))
-            && !$event->getRequest()->headers->has('X-FirePHP-Version')) {
-            $this->sendHeaders = false;
+        $request = $event->getRequest();
+        if (!preg_match('{\bFirePHP/\d+\.\d+\b}', $request->headers->get('User-Agent'))
+            && !$request->headers->has('X-FirePHP-Version')) {
+            self::$sendHeaders = false;
             $this->headers = array();
 
             return;
@@ -58,7 +59,7 @@ public function onKernelResponse(FilterResponseEvent $event)
      */
     protected function sendHeader($header, $content)
     {
-        if (!$this->sendHeaders) {
+        if (!self::$sendHeaders) {
             return;
         }