src/vs/workbench/browser/layout.ts/Layout/hasFocus
class Layout:	hasFocus(part: Parts): boolean {
		const activeElement = document.activeElement;
		if (!activeElement) {
			return false;
		}

		const container = this.getContainer(part);

		return !!container && isAncestorUsingFlowTo(activeElement, container);
	}