src/vs/workbench/contrib/preferences/browser/settingsEditor2.ts/SettingsEditor2/getActiveControlInSettingsTree
class SettingsEditor2:	private getActiveControlInSettingsTree(): HTMLElement | null {
		return (document.activeElement && DOM.isAncestor(document.activeElement, this.settingsTree.getHTMLElement())) ?
			<HTMLElement>document.activeElement :
			null;
	}