Check whether it's a file url and iOS 8, and use loadHTMLString to present an error instead (and NSLog it).
This is unfortunate and shouldn't happen but we need to catch it nonetheless.
The WebView engine load will fail if these conditions are fulfilled:
1. iOS 8
2. file:// url
3. current WebView engine is a WKWebView
This determination should be delegated to the WebView engine itself. There needs to be another method in the CDVWebViewEngineProtocol – canLoadRequest:(NSURLRequest*)
If the WebViewEngine cannot load the request, we fall back to the UIWebView engine. This might cause a UI glitch that is undesirable when we need to replace WebView engines – this assumption needs to be tested.