Use headless WebViewManager on headless clients.

Robust.Client.WebView/Headless/WebViewManagerHeadless.cs

@@ -0,0 +1,127 @@
+using System;
+using Robust.Client.Graphics;
+using Robust.Client.UserInterface;
+
+namespace Robust.Client.WebView.Headless
+{
+    internal sealed class WebViewManagerHeadless : IWebViewManagerImpl
+    {
+        public IWebViewWindow CreateBrowserWindow(BrowserWindowCreateParameters createParams)
+        {
+            return new WebViewWindowDummy();
+        }
+
+        public IWebViewControlImpl MakeControlImpl(WebViewControl owner)
+        {
+            return new WebViewControlImplDummy();
+        }
+
+        public void Initialize()
+        {
+            // Nop
+        }
+
+        public void Update()
+        {
+            // Nop
+        }
+
+        public void Shutdown()
+        {
+            // Nop
+        }
+
+        private abstract class DummyBase : IWebViewControl
+        {
+            public string Url { get; set; } = "about:blank";
+            public bool IsLoading => true;
+
+            public void StopLoad()
+            {
+            }
+
+            public void Reload()
+            {
+            }
+
+            public bool GoBack()
+            {
+                return false;
+            }
+
+            public bool GoForward()
+            {
+                return false;
+            }
+
+            public void ExecuteJavaScript(string code)
+            {
+            }
+
+            public void AddResourceRequestHandler(Action<IRequestHandlerContext> handler)
+            {
+            }
+
+            public void RemoveResourceRequestHandler(Action<IRequestHandlerContext> handler)
+            {
+            }
+        }
+
+        private sealed class WebViewControlImplDummy : DummyBase, IWebViewControlImpl
+        {
+            public void EnteredTree()
+            {
+            }
+
+            public void ExitedTree()
+            {
+            }
+
+            public void MouseMove(GUIMouseMoveEventArgs args)
+            {
+            }
+
+            public void MouseExited()
+            {
+            }
+
+            public void MouseWheel(GUIMouseWheelEventArgs args)
+            {
+            }
+
+            public bool RawKeyEvent(in GuiRawKeyEvent guiRawEvent)
+            {
+                return false;
+            }
+
+            public void TextEntered(GUITextEventArgs args)
+            {
+            }
+
+            public void Resized()
+            {
+            }
+
+            public void Draw(DrawingHandleScreen handle)
+            {
+            }
+
+            public void AddBeforeBrowseHandler(Action<IBeforeBrowseContext> handler)
+            {
+            }
+
+            public void RemoveBeforeBrowseHandler(Action<IBeforeBrowseContext> handler)
+            {
+            }
+        }
+
+        private sealed class WebViewWindowDummy : DummyBase, IWebViewWindow
+        {
+            public void Dispose()
+            {
+            }
+
+            public bool Closed => false;
+        }
+    }
+}

Robust.Client.WebView/IWebViewManagerImpl.cs

@@ -5,8 +5,10 @@ namespace Robust.Client.WebView
     /// <summary>
     /// Internal implementation of WebViewManager that is switched out by <see cref="IWebViewManagerHook"/>.
     /// </summary>
-    internal interface IWebViewManagerImpl : IWebViewManagerInternal, IWebViewManagerHook
+    internal interface IWebViewManagerImpl : IWebViewManagerInternal
     {
-
+        void Initialize();
+        void Update();
+        void Shutdown();
     }
 }

Robust.Client.WebView/WebViewManager.cs

@@ -1,5 +1,6 @@
 using Robust.Client.WebView;
 using Robust.Client.WebView.Cef;
+using Robust.Client.WebView.Headless;
 using Robust.Client.WebViewHook;
 using Robust.Shared.IoC;
 using Robust.Shared.Utility;
@@ -12,14 +13,18 @@ namespace Robust.Client.WebView
     {
         private IWebViewManagerImpl? _impl;
 
-        public void Initialize()
+        public void Initialize(GameController.DisplayMode mode)
         {
             DebugTools.Assert(_impl == null, "WebViewManager has already been initialized!");
 
             IoCManager.RegisterInstance<IWebViewManager>(this);
             IoCManager.RegisterInstance<IWebViewManagerInternal>(this);
 
-            _impl = new WebViewManagerCef();
+            if (mode == GameController.DisplayMode.Headless)
+                _impl = new WebViewManagerHeadless();
+            else
+                _impl = new WebViewManagerCef();
+
             _impl.Initialize();
         }