Set credentials mode "same-origin" when crossOrigin=anonymous is set.

third_party/WebKit/LayoutTests/http/tests/security/resources/abe-allow-credentials.php

 <?php
+$cookie_check = $_GET["Cookie"];
+if (isset($cookie_check)) {
+  if ($cookie_check == "NotSet") {
+    if (isset($_COOKIE['TestCookie'])) {
+      header("HTTP/1.0 404 Not Found");
+      exit;
+    }
+  } else if ($cookie_check != $_COOKIE['TestCookie']) {
+    header("HTTP/1.0 404 Not Found");
+    exit;
+  }
+}
+
 header("Access-Control-Allow-Origin: http://127.0.0.1:8000");
 header("Access-Control-Allow-Credentials: true");
 
 $name = 'abe.png';
 $fp = fopen($name, 'rb');
 header("Content-Type: image/png");
 header("Content-Length: " . filesize($name));
 
 fpassthru($fp);
 exit;
 ?>