When we use UWP's WebView class we get a marshalling exception.

System.Runtime.InteropServices.MarshalDirectiveException: Cannot marshal type 'System.Uri'.
at Windows.UI.Xaml.Controls.WebView.Navigate (System.Uri source) [0x00000] in <00000000000000000000000000000000>:0
at WSAUnity.Plugins.ShowWebView (System.Double x, System.Double y, System.Double width, System.Double height, System.String url, System.Action`1[T] callback) [0x00000] in <00000000000000000000000000000000>:0
at Webview.<Start>b__2_0 () [0x00000] in <00000000000000000000000000000000>:0
at UnityEngine.WSA.AppCallbackItem.Invoke () [0x00000] in <00000000000000000000000000000000>:0

Forum thread: https://forum.unity3d.com/threads/uwp-il2cpp-and-xaml-controls.457862/