Add named constructor on JsonResponse

To make easier construction with raw json

src/Symfony/Component/HttpFoundation/JsonResponse.php

@@ -58,6 +58,14 @@ class JsonResponse extends Response
         return new static($data, $status, $headers);
     }
 
+    /**
+     * Make easier the creation of JsonResponse from raw json.
+     */
+    public static function fromJsonString($data = null, $status = 200, $headers = array())
+    {
+        return new static($data, $status, $headers, true);
+    }
+
     /**
      * Sets the JSONP callback.
      *

src/Symfony/Component/HttpFoundation/Tests/JsonResponseTest.php

@@ -198,6 +198,12 @@ class JsonResponseTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals('{"0":{"0":1,"1":2,"2":3}}', $response->getContent());
     }
 
+    public function testItAcceptsJsonAsString()
+    {
+        $response = JsonResponse::fromJsonString('{"foo":"bar"}');
+        $this->assertSame('{"foo":"bar"}', $response->getContent());
+    }
+
     /**
      * @expectedException \InvalidArgumentException
      */