Trying to shoehorn pending actions into the PendingDownloadActions queue
doesn't work unless you use a unique download ID. Just store a separate
int that tracks what downloads have been requested.
Fix SSLUITest.TestGoodFrameNavigation with PlzNavigate.
The problem was that this test was checking that it got the notification that insecure content was run. Without PlzNavigate, this notification was sent from the renderer before it starts loading the url (http://example.test/...). The content never actually loaded, because browser tests have a resolver that block all network requests to the outside world in order to avoid flaky tests which make network requests. With PlzNavigate, the request was being cancelled in the browser process and the renderer never got as far to be told that insecure content was run.
The fix is to just the browser test to treat example.test as a local host. A small side effect is that it now also loads the image in that page, so we need to tweak the test to reflect that the page both loads and displays insecure content.
