Read the Cookie response headers from a `white-space: pre' element so that any white-space in them would be preserved in the expectation value

Differential Revision: https://phabricator.services.mozilla.com/D32239

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1553680
gecko-commit: 7a039c35fc6f96e13d1a24c54139c942902ee5a4
gecko-integration-branch: autoland
gecko-reviewers: baku
diff --git a/cookies/http-state/resources/iframe-expectation-doc.html.py-str b/cookies/http-state/resources/iframe-expectation-doc.html.py-str
index f2cf313..9b782a1 100644
--- a/cookies/http-state/resources/iframe-expectation-doc.html.py-str
+++ b/cookies/http-state/resources/iframe-expectation-doc.html.py-str
@@ -5,7 +5,7 @@
     <title>Cookie Test Expectation Document</title>
   </head>
   <body>
-    <div id="data">{data}</div>
+    <div id="data" style="white-space: pre">{data}</div>
     <script src="iframe-content-pushing.js"></script>
   </body>
 </html>