Disable clipboard button with async clipboard

With async clipboard available, the fallback clipboard textarea adds
mostly confusion. If async clipboard is out right denied, users most
likely don't want to see any clipboard activity.

app/ui.js

@@ -9,7 +9,7 @@
 import * as Log from '../core/util/logging.js';
 import _, { l10n } from './localization.js';
 import { isTouchDevice, isMac, isIOS, isAndroid, isChromeOS, isSafari,
-         hasScrollbarGutter, dragThreshold }
+         hasScrollbarGutter, dragThreshold, browserAsyncClipboardSupport }
     from '../core/util/browser.js';
 import { setCapture, getPointerEvent } from '../core/util/events.js';
 import KeyTable from "../core/input/keysym.js";
@@ -1103,6 +1103,7 @@ const UI = {
         UI.rfb.showDotCursor = UI.getSetting('show_dot');
 
         UI.updateViewOnly(); // requires UI.rfb
+        UI.updateClipboard();
     },
 
     disconnect() {
@@ -1754,6 +1755,31 @@ const UI = {
         }
     },
 
+    updateClipboard() {
+        browserAsyncClipboardSupport()
+            .then((support) => {
+                if (support === 'unsupported') {
+                    // Use fallback clipboard panel
+                    return;
+                }
+                if (support === 'denied' || support === 'available') {
+                    UI.closeClipboardPanel();
+                    document.getElementById('noVNC_clipboard_button')
+                        .classList.add('noVNC_hidden');
+                    document.getElementById('noVNC_clipboard_button')
+                        .removeEventListener('click', UI.toggleClipboardPanel);
+                    document.getElementById('noVNC_clipboard_text')
+                        .removeEventListener('change', UI.clipboardSend);
+                    if (UI.rfb) {
+                        UI.rfb.removeEventListener('clipboard', UI.clipboardReceive);
+                    }
+                }
+            })
+            .catch(() => {
+                // Treat as unsupported
+            });
+    },
+
     updateShowDotCursor() {
         if (!UI.rfb) return;
         UI.rfb.showDotCursor = UI.getSetting('show_dot');