While working on the DevTools profiler, I've noticed that durations are sometimes incorrect. This seems to be vaguely related to high/low priority state updates. Need to track this down more so I'm filing an issue for myself.
REACT_PROFILER_TYPE,
  REACT_PROVIDER_TYPE,
  REACT_CONTEXT_TYPE,
  REACT_ASYNC_MODE_TYPE,
  REACT_PLACEHOLDER_TYPE,
} from 'shared/ReactSymbols';
let hasBadMapPolyfill;
if (__DEV__) {
  hasBadMapPolyfill = false;
  try {
    const nonExtensibleObject = Object.preventExtensions({});
    const testMap = new Map([[nonExtensibleObject, null]]);
    const testSet = new Set([nonExtensibleObject]);
    
    
    
    testMap.set(0, 0);
    testSet.add(0);
  } catch (e) {
    
    hasBadMapPolyfill = true;
  }
}
export type Fiber = {|