src/vs/workbench/browser/parts/panel/panelPart.ts/BasePanelPart/onPanelClose
class BasePanelPart:	private onPanelClose(panel: IComposite): void {
		const id = panel.getId();

		if (this.activePanelContextKey.get() === id) {
			this.activePanelContextKey.reset();
		}

		this.compositeBar.deactivateComposite(panel.getId());
		this.layoutEmptyMessage();
	}