fix system context menu handler is not registered (microsoft#155533)

* fix system context menu handler is not registered

* fix hygiene

Author: sbatten

src/vs/workbench/electron-sandbox/parts/titlebar/titlebarPart.ts

@@ -196,19 +196,19 @@ export class TitlebarPart extends BrowserTitleBarPart {
 
 			this._register(this.layoutService.onDidChangeWindowMaximized(maximized => this.onDidChangeWindowMaximized(maximized)));
 			this.onDidChangeWindowMaximized(this.layoutService.isWindowMaximized());
+		}
 
-			// Window System Context Menu
-			// See https://github.com/electron/electron/issues/24893
-			if (isWindows) {
-				this._register(this.nativeHostService.onDidTriggerSystemContextMenu(({ windowId, x, y }) => {
-					if (this.nativeHostService.windowId !== windowId) {
-						return;
-					}
-
-					const zoomFactor = getZoomFactor();
-					this.onContextMenu(new MouseEvent('mouseup', { clientX: x / zoomFactor, clientY: y / zoomFactor }), MenuId.TitleBarContext);
-				}));
-			}
+		// Window System Context Menu
+		// See https://github.com/electron/electron/issues/24893
+		if (isWindows && getTitleBarStyle(this.configurationService) === 'custom') {
+			this._register(this.nativeHostService.onDidTriggerSystemContextMenu(({ windowId, x, y }) => {
+				if (this.nativeHostService.windowId !== windowId) {
+					return;
+				}
+
+				const zoomFactor = getZoomFactor();
+				this.onContextMenu(new MouseEvent('mouseup', { clientX: x / zoomFactor, clientY: y / zoomFactor }), MenuId.TitleBarContext);
+			}));
 		}
 
 		return ret;