Fix kernel access in HttpCache due to kernel attribute privatization

src/Symfony/Bundle/FrameworkBundle/HttpCache/HttpCache.php

@@ -49,9 +49,9 @@ abstract class HttpCache extends BaseHttpCache
      */
     protected function forward(Request $request, $raw = false, Response $entry = null)
     {
-        $this->kernel->boot();
-        $this->kernel->getContainer()->set('cache', $this);
-        $this->kernel->getContainer()->set('esi', $this->esi);
+        $this->getKernel()->boot();
+        $this->getKernel()->getContainer()->set('cache', $this);
+        $this->getKernel()->getContainer()->set('esi', $this->esi);
 
         return parent::forward($request, $raw, $entry);
     }

src/Symfony/Component/HttpKernel/HttpCache/HttpCache.php

@@ -128,6 +128,16 @@ class HttpCache implements HttpKernelInterface
         return $this->request;
     }
 
+    /**
+     * Gets the Kernel instance
+     *
+     * @return Symfony\Component\HttpKernel\HttpKernelInterface An HttpKernelInterface instance
+     */
+    public function getKernel()
+    {
+        return $this->kernel;
+    }
+
     /**
      * {@inheritdoc}
      */