Fix test: http/tests/navigation/back-send-referrer.html

The navigation may be triggered before the load event. When it happens,
the history entry must replace the current one instead of being appended
to it. Then history.go(-1) fails in the next document.

This CL make the navigation to happen after the load event.

Bug: 862580, 831155
Change-Id: I4a48d50f5899e3fd65c74d9a89ab836ae94ba7be
Reviewed-on: https://chromium-review.googlesource.com/1133261Reviewed-by: Nate Chapin <japhet@chromium.org>
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578998}

third_party/WebKit/LayoutTests/http/tests/navigation/back-send-referrer.html

@@ -4,6 +4,10 @@
         testRunner.dumpAsText();
     }
 
-    window.name = "0";
-    window.location = "resources/back-send-referrer-helper.php";
+    window.onload = function() {
+        setTimeout(function() {
+            window.name = "0";
+            window.location = "resources/back-send-referrer-helper.php"
+        }, 0);
+    }
 </script>