Add layout tests about sendBeacon's handling of credentials for cross origin redirects

third_party/WebKit/LayoutTests/http/tests/navigation/resources/save-beacon.php

Index: third_party/WebKit/LayoutTests/http/tests/navigation/resources/save-beacon.php
diff --git a/third_party/WebKit/LayoutTests/http/tests/navigation/resources/save-beacon.php b/third_party/WebKit/LayoutTests/http/tests/navigation/resources/save-beacon.php
index a43ff62c29929a8604040105ebf7b80ebe87d535..1888c9329cc5bdbd380cf21a39a513310e89488e 100644
--- a/third_party/WebKit/LayoutTests/http/tests/navigation/resources/save-beacon.php
+++ b/third_party/WebKit/LayoutTests/http/tests/navigation/resources/save-beacon.php
@@ -32,6 +32,9 @@ if (strpos($contentType, "application/") !== false) {
 fwrite($beaconFile, "Body: $postdata\n");
 fclose($beaconFile);
 rename($beaconFilename . ".tmp", $beaconFilename);
-foreach ($_COOKIE as $name => $value)
-    setcookie($name, "deleted", time() - 60, "/");
+
+if (!array_key_exists('dontclearcookies', $_GET)) {
+  foreach ($_COOKIE as $name => $value)
+      setcookie($name, "deleted", time() - 60, "/");
+}
 ?>