Got this debugging another error. Filing here for reference. Original code: https://phabricator.intern.facebook.com/P59317705
'or forceUpdate on an unmounted component. This is a no-op.\n\nPlease ' +
        'check the code for the %s component.',
      componentName,
    );
    didWarnStateUpdateForUnmountedComponent[componentName] = true;
  };
  warnAboutInvalidUpdates = function(instance: React$Component<any>) {
    switch (ReactDebugCurrentFiber.phase) {
      case 'getChildContext':
        if (didWarnSetStateChildContext) {
          return;
        }
        warning(
          false,
          'setState(...): Cannot call setState() inside getChildContext()',
        );
        didWarnSetStateChildContext = true;
        break;
      case 'render':
        if (didWarnAboutStateTransition) {
          return;
        }
        warning(
          false,
          'Cannot update during an existing state transition (such as within ' +
            "`render` or another component's constructor). Render methods should " +
            'be a pure function of props and state; constructor side-effects are ' +
            'an anti-pattern, but can be moved to `componentWillMount`.',
        );
        didWarnAboutStateTransition = true;