Allow <webview> to access URLs in the origin of the app embedding it.

chrome/test/data/extensions/platform_apps/web_view/guest_focus_test/guest.js

Index: chrome/test/data/extensions/platform_apps/web_view/guest_focus_test/guest.js
diff --git a/chrome/test/data/extensions/platform_apps/web_view/guest_focus_test/guest.js b/chrome/test/data/extensions/platform_apps/web_view/guest_focus_test/guest.js
index 5a8b67fa32e9d9bf43d25bcab13b38b00b0f04b4..55ed45077a7a0da71b5ece052757fc8a2669e5ca 100644
--- a/chrome/test/data/extensions/platform_apps/web_view/guest_focus_test/guest.js
+++ b/chrome/test/data/extensions/platform_apps/web_view/guest_focus_test/guest.js
@@ -17,6 +17,7 @@ function sendMessageToEmbedder(message) {
 }
 
 window.addEventListener('message', function(e) {
+  URL.createObjectURL(new Blob([]));

[lazyboy, 2016/10/04 22:15:31]

This seems unrelated to this test.
If you're in a rush, you should at least put a comment and a TODO to extract
this to a separate test.

   embedder = e.source;
   var data = JSON.parse(e.data);
   if (data[0] == 'connect') {