src/vs/platform/instantiation/common/instantiationService.ts/InstantiationService/_getServiceInstanceOrDescriptor
class InstantiationService:	private _getServiceInstanceOrDescriptor<T>(id: ServiceIdentifier<T>): T | SyncDescriptor<T> {
		const instanceOrDesc = this._services.get(id);
		if (!instanceOrDesc && this._parent) {
			return this._parent._getServiceInstanceOrDescriptor(id);
		} else {
			return instanceOrDesc;
		}
	}