Web - try to detect native fullscreen (#106479)

* web - try to detect native fullscreen

* add logging for debugging

* throttle listener

* adjust

* .

* add check for windows

src/vs/base/browser/dom.ts

@@ -1277,3 +1277,66 @@ export function triggerDownload(dataOrUri: Uint8Array | URI, name: string): void
 	// Ensure to remove the element from DOM eventually
 	setTimeout(() => document.body.removeChild(anchor));
 }
+
+export enum DetectedFullscreenMode {
+
+	/**
+	 * The document is fullscreen, e.g. because an element
+	 * in the document requested to be fullscreen.
+	 */
+	DOCUMENT = 1,
+
+	/**
+	 * The browser is fullsreen, e.g. because the user enabled
+	 * native window fullscreen for it.
+	 */
+	BROWSER
+}
+
+export interface IDetectedFullscreen {
+
+	/**
+	 * Figure out if the document is fullscreen or the browser.
+	 */
+	mode: DetectedFullscreenMode;
+
+	/**
+	 * Wether we know for sure that we are in fullscreen mode or
+	 * it is a guess.
+	 */
+	guess: boolean;
+}
+
+export function detectFullscreen(): IDetectedFullscreen | null {
+
+	// Browser fullscreen: use DOM APIs to detect
+	if (document.fullscreenElement || (<any>document).webkitFullscreenElement || (<any>document).webkitIsFullScreen) {
+		return { mode: DetectedFullscreenMode.DOCUMENT, guess: false };
+	}
+
+	// There is no standard way to figure out if the browser
+	// is using native fullscreen. Via checking on screen
+	// height and comparing that to window height, we can guess
+	// it though.
+
+	if (window.innerHeight === screen.height) {
+		// if the height of the window matches the screen height, we can
+		// safely assume that the browser is fullscreen because no browser
+		// chrome is taking height away (e.g. like toolbars).
+		return { mode: DetectedFullscreenMode.BROWSER, guess: false };
+	}
+
+	if (platform.isMacintosh || platform.isLinux) {
+		// macOS and Linux do not properly report `innerHeight`, only Windows does
+		if (window.outerHeight === screen.height && window.outerWidth === screen.width) {
+			// if the height of the browser matches the screen height, we can
+			// only guess that we are in fullscreen. It is also possible that
+			// the user has turned off taskbars in the OS and the browser is
+			// simply able to span the entire size of the screen.
+			return { mode: DetectedFullscreenMode.BROWSER, guess: true };
+		}
+	}
+
+	// Not in fullscreen
+	return null;
+}