This DEV-only field was added in 836331ba5f69f2cc53b273ec073fae116db14302 by @sebmarkbage but it's not being used anymore to my knowledge.
next: ContextDependency<mixed> | null,
  memoizedValue: T,
  ...
};
export type Dependencies = {
  lanes: Lanes,
  firstContext: ContextDependency<mixed> | null,
  ...
};
export type Fiber = {|
  
  
  
  
  
  
  
  
  
  tag: WorkTag,
  
  key: null | string,
  
  
  elementType: any,
  
  type: any,
  
  stateNode: any,