Allow swapping out internal WebViewManager implementation.

Everything moved to interfaces.

Robust.Client.WebView/Cef/CefBeforeBrowseContext.cs

@@ -0,0 +1,32 @@
+using Xilium.CefGlue;
+
+namespace Robust.Client.WebView.Cef
+{
+    internal sealed class CefBeforeBrowseContext : IBeforeBrowseContext
+    {
+        internal readonly CefRequest CefRequest;
+
+        public string Url => CefRequest.Url;
+        public string Method => CefRequest.Method;
+
+        public bool IsRedirect { get; }
+        public bool UserGesture { get; }
+
+        public bool IsCancelled { get; private set; }
+
+        internal CefBeforeBrowseContext(
+            bool isRedirect,
+            bool userGesture,
+            CefRequest cefRequest)
+        {
+            CefRequest = cefRequest;
+            IsRedirect = isRedirect;
+            UserGesture = userGesture;
+        }
+
+        public void DoCancel()
+        {
+            IsCancelled = true;
+        }
+    }
+}