Rework EventSource CORS tests to be usable from Workers.

LayoutTests/http/tests/resources/redirect.php

Index: LayoutTests/http/tests/resources/redirect.php
diff --git a/LayoutTests/http/tests/resources/redirect.php b/LayoutTests/http/tests/resources/redirect.php
index cfeb37d1c56f4e24fde8f2bb07ad4c4a15cf0f83..08d274509d7bc95157c3110059f26730c7916c62 100644
--- a/LayoutTests/http/tests/resources/redirect.php
+++ b/LayoutTests/http/tests/resources/redirect.php
@@ -1,16 +1,19 @@
 <?php
     $url = $_GET['url'];
     $refresh = $_GET['refresh'];
-    
+
     if (isset($refresh)) {
         header("HTTP/1.1 200");
         header("Refresh: $refresh; url=$url");
         return;
     }
 
+    header("Location: $url");
+    if (isset($_GET['cors_allow_origin']))
+        header("Access-Control-Allow-Origin: " . $_GET['cors_allow_origin']);
+
     $code = $_GET['code'];
     if (!isset($code))
         $code = 302;
     header("HTTP/1.1 $code");
-    header("Location: $url");
 ?>