Subclassing a WKWebView in Swift, non-functional as of Xcode6-Beta6

TestWebView.swift

import Cocoa
import WebKit

class TestWebView : WKWebView {

    override init(frame frameRect: NSRect) {
        super.init(frame: frameRect, configuration: WKWebViewConfiguration())
    }

    override init(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
}