predictors: Add browsertests that check fetching through javascript.

chrome/test/data/predictors/append_child.js

Index: chrome/test/data/predictors/append_child.js
diff --git a/chrome/test/data/predictors/append_child.js b/chrome/test/data/predictors/append_child.js
new file mode 100644
index 0000000000000000000000000000000000000000..7c632ee52d098e3dfcaeaed120ed10c3fcff6e3b
--- /dev/null
+++ b/chrome/test/data/predictors/append_child.js
@@ -0,0 +1,12 @@
+var img = document.createElement("img");
+img.src = "/handled-by-test/image.png"
+document.body.appendChild(img);
+
+var link = document.createElement("link");
+link.rel = "stylesheet";
+link.href = "/handled-by-test/style.css";
+document.head.appendChild(link);
+
+var script = document.createElement("script");
+script.src = "/handled-by-test/script.js";
+document.body.appendChild(script);