Site doesn't show up in the graph view when the Lightbeam tab is hidden

[fmarier]

Steps to reproduce:

1. in a fresh profile, install Lightbeam
2. leave the Lightbeam tab closed (i.e. don't click on the Lightbeam icon)
3. visit https://HillaryClinton.com
4. open Lightbeam

Expected:

The site and its third-party resources show up both in the graph and list views.

Actual:

The site only shows up in the list view, the graph view is empty.

Note: if I open the Lightbeam tab before visiting the site, then it works as expected.