This was an existing test, although I'm not entirely sure how the client.goUrl stuff was working.  We cause the browser to load index.html which includes an iframe which references frame.html.  frame.html is the one that actually does the console.log.  This is a nice test since the content page should be loaded in a mozbrowser and if OOP is happening (not yet on linux, but soon), this tests that we properly see the messages from the subprocess.  (Which is pretty important because I'm not actually confident that the console messages will be relayed; a cursory investigation of the native code suggests they do not get relayed and we may need to explicitly attach to and poll the frame of interest.)

The nested iframe doesn't actually do anything notable, but does add some nice extra thoroughness.  I suppose we could also test a worker, too, since those are supported and should categorically work.