predictors: Add browsertests that check fetching through javascript.

chrome/test/data/predictors/xhr.js

Index: chrome/test/data/predictors/xhr.js
diff --git a/chrome/test/data/predictors/xhr.js b/chrome/test/data/predictors/xhr.js
new file mode 100644
index 0000000000000000000000000000000000000000..266fa37aa7d59f48f32ac916fea23aa6b64911da
--- /dev/null
+++ b/chrome/test/data/predictors/xhr.js
@@ -0,0 +1,13 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+function requestSynchronously(url) {
+  var request = new XMLHttpRequest();
+  request.open('GET', url, false);
+  request.send(null);
+}
+
+requestSynchronously('/handled-by-test/image.png');
+requestSynchronously("/handled-by-test/style.css");
+requestSynchronously("/handled-by-test/script.js");