Update ExternalPopUpTest to check number examined elements

This test was incorrectly checking the state flow graph.  Now it checks
to make sure only the correct number of elements are examined based on
the test site.
Use correct getter function

The isExternal function had been renamed and this reference was still
lingering.
Execute javascript code to check for window.open

In the event that an element's onclick is a function, the function needs
to be searched for a window.open call.