src/vs/workbench/browser/parts/panel/panelPart.ts/BasePanelPart/onDidPaneCompositeOpen
class BasePanelPart:	get onDidPaneCompositeOpen(): Event<IPaneComposite> { return Event.map(this.onDidCompositeOpen.event, compositeEvent => <IPaneComposite>compositeEvent.composite); }