Fix plugin sandbox permissions

Add `allow-same-origin` to the iframe sandbox attribute.  This allows
plugins to share the origin with the application, enabling access to
session cookies and fixing CORS failures in strict browsers (Firefox,
Safari).

Change-Id: Ic3ff8a343f406a44cc673097f0eeb2be74050f5b
diff --git a/dev/js/src/plugin/service.js b/dev/js/src/plugin/service.js
index d6af83e..aa00182 100644
--- a/dev/js/src/plugin/service.js
+++ b/dev/js/src/plugin/service.js
@@ -70,7 +70,9 @@
       e.setAttribute('allowTransparency',"true");
       e.setAttribute('frameborder', 0);
       // Allow forms in Plugins
-      e.setAttribute('sandbox', Array.from(this._perm).sort().map(function(i){ return "allow-"+i }).join(" "));
+      let permissions = Array.from(this._perm).sort().map(function(i){ return "allow-"+i });
+      permissions.push("allow-same-origin");
+      e.setAttribute('sandbox', permissions.join(" "));
       e.style.height = '0px';
       e.setAttribute('name', this.id);
       e.setAttribute('src', this.src);