src/vs/platform/instantiation/common/instantiationService.ts/InstantiationService/_setServiceInstance
class InstantiationService:	private _setServiceInstance<T>(id: ServiceIdentifier<T>, instance: T): void {
		if (this._services.get(id) instanceof SyncDescriptor) {
			this._services.set(id, instance);
		} else if (this._parent) {
			this._parent._setServiceInstance(id, instance);
		} else {
			throw new Error('illegalState - setting UNKNOWN service instance');
		}
	}