Instantiate WebView via NSClassFromString.

[FabioSpacagna]

I know this is not real project but consider that this small fix will make the life more easy to newbies and anyone not familiar with Availability.h vi or nano.

Basically i have applied the elegant fix suggested by zachhowe (id + NSClassFromString) to trick the compiler.

This will solve the issue "Changes to Availability.h."

[Jason-Morcos]

@FabioSpacagna: Last I heard, this branch was no longer being maintained. I run a branch that is maintained and includes those changes you suggested. https://github.com/Moballo-LLC/tvOS-Browser