changing url has no effect on existing WebviewScaffold.

[sma]

My setup uses two WebviewScaffolds with different urls in such a way that Flutter will not rebuild the WebviewScaffold widget but simply change the properties. Neither initState nor dispose is called and therefore the plugin will not notice that the URL has been changed. Please also implement didUpdateWidget to deal with that fact.

The implementation below seems to work but I don't know whether it is okay to simply copy the rather longish call from build. I tried to call webviewReference.reloadUrl but that didn't work.

  @override
  void didUpdateWidget(WebviewScaffold oldWidget) {
    super.didUpdateWidget(oldWidget);
    if (oldWidget.url != widget.url) {
      webviewReference.launch(widget.url,
        headers: widget.headers,
        withJavascript: widget.withJavascript,
        clearCache: widget.clearCache,
        clearCookies: widget.clearCookies,
        enableAppScheme: widget.enableAppScheme,
        userAgent: widget.userAgent,
        rect: _rect,
        withZoom: widget.withZoom,
        withLocalStorage: widget.withLocalStorage,
        withLocalUrl: widget.withLocalUrl,
        scrollBar: widget.scrollBar);
    }
  }

[slightfoot]

Duplicate of #174