[HttpClient] Adding missing dependency for dev

Author: Nyholm

composer.json

@@ -39,7 +39,8 @@
         "psr/http-client": "^1.0",
         "symfony/dependency-injection": "^4.4|^5.0",
         "symfony/http-kernel": "^4.4.13|^5.1.5",
-        "symfony/process": "^4.4|^5.0"
+        "symfony/process": "^4.4|^5.0",
+        "symfony/stopwatch": "^4.4|^5.0"
     },
     "autoload": {
         "psr-4": { "Symfony\\Component\\HttpClient\\": "" },