Same-site BFCache

Creating this issue to investigate changes introduced by https://bitbucket.org/chromiumembedded/cef/commits/54dd34e19b56a2b7f0d6cb8d473ce36288dcf8e2

> BFCache navigations do not trigger the same Chromium notifications as a normal
load. To avoid breaking CEF API usage expectations we now synthetically
generate the load-related callbacks that would otherwise be missing
(OnLoadingStateChange with isLoading=true, OnLoadStart, OnLoadEnd). The
|httpStatusCode| argument to OnLoadEnd will be 0 in this case.

`LoadUrlAsync` needs to be reviewed in light of these changes.

https://github.com/cefsharp/CefSharp/blob/8927a335036125002065ae0f171e7386bf34b45f/CefSharp/WebBrowserExtensions.cs#L443