Bug 258711

If a content blocking rule with `make-https` upgrades a subresource from http:// to https://, webkit still reports `hasOnlySecureContent=false` even if the page never loads any http:// resource.

Here is a sample app (the whole repo should be buildable): https://github.com/meacer/swift-ios-wkwebview-demo-make-https/blob/master/wkwebview/ViewController.swift

In this app, line 63 will print `hasOnlySecureContent: false` even though the image subresource is loaded over https.

(We recently implemented mixed content upgrading in Chromium on iOS using a make-https content rule, and this bug is preventing us from showing the correct page security state in the omnibox.)