src/vs/workbench/contrib/webviewPanel/browser/webviewEditor.ts/WebviewEditor/trackFocus
class WebviewEditor:	private trackFocus(webview: WebviewOverlay): IDisposable {
		const store = new DisposableStore();

		// Track focus in webview content
		const webviewContentFocusTracker = DOM.trackFocus(webview.container);
		store.add(webviewContentFocusTracker);
		store.add(webviewContentFocusTracker.onDidFocus(() => this._onDidFocusWebview.fire()));

		// Track focus in webview element
		store.add(webview.onDidFocus(() => this._onDidFocusWebview.fire()));

		return store;
	}