Add Keyboard Lock API support (Chromium 68+ & HTTPS only)

This enables web browser to capture key combos, e.g., Alt+F4, Alt+Tab, and send it to web page.

Limitations: 1) Chromium 68+ only; 2) User should click full screen button inside the webpage. API won't work when toggling full screen via F11 or browser menu. 3) HTTPS instead of HTTP.

- https://developer.chrome.com/docs/capabilities/web-apis/keyboard-lock
- https://developer.mozilla.org/en-US/docs/Web/API/Navigator/keyboard

app/ui.js

@@ -29,7 +29,7 @@ import "core-js/stable";
 import "regenerator-runtime/runtime";
 import * as Log from '../core/util/logging.js';
 import _, { l10n } from './localization.js';
-import { isTouchDevice, isSafari, hasScrollbarGutter, dragThreshold, supportsBinaryClipboard, isFirefox, isWindows, isIOS, supportsPointerLock }
+import { isTouchDevice, isSafari, hasScrollbarGutter, dragThreshold, supportsBinaryClipboard, isFirefox, isWindows, isIOS, supportsPointerLock, supportsKeyboardLock }
     from '../core/util/browser.js';
 import { setCapture, getPointerEvent } from '../core/util/events.js';
 import KeyTable from "../core/input/keysym.js";
@@ -1841,6 +1841,9 @@ const UI = {
             document.mozFullScreenElement || // currently working methods
             document.webkitFullscreenElement ||
             document.msFullscreenElement) {
+            if (supportsKeyboardLock) {
+                navigator.keyboard.unlock();
+            }
             if (document.exitFullscreen) {
                 document.exitFullscreen();
             } else if (document.mozCancelFullScreen) {
@@ -1860,6 +1863,12 @@ const UI = {
             } else if (document.body.msRequestFullscreen) {
                 document.body.msRequestFullscreen();
             }
+            // No need to explicitly ask for permission,
+            // but it's expected that user grant it since Chromium 131.
+            // See https://developer.chrome.com/blog/keyboard-lock-pointer-lock-permission
+            if (supportsKeyboardLock) {
+                navigator.keyboard.lock();
+            }
         }
         UI.updateFullscreenButton();
     },

core/util/browser.js

@@ -27,6 +27,8 @@ window.addEventListener('touchstart', function onFirstTouch() {
 // brings us a bit closer but is not optimal.
 export let dragThreshold = 10 * (window.devicePixelRatio || 1);
 
+export const supportsKeyboardLock = ('keyboard' in navigator && 'lock' in navigator.keyboard && typeof(navigator.keyboard.lock) === 'function');
+
 let _supportsCursorURIs = false;
 
 try {
@@ -174,4 +176,3 @@ export function supportsPointerLock() {
     if (isIOS() || isIE()) { return false; }
     return (document.exitPointerLock);
 }
-