(Regarding the experimental `React.unstable_Profiler` API and reactjs/rfcs/pull/51.)

PR #13058 changed the behavior of React profiling builds to opt host roots into `ProfileMode` if the React DevTools extension is detected. This was necessary in order to have accurate tree base time measurements for the visual flame graphs.

The Profiler plug-in for DevTools does feature detection to determine if it's enabled by looking at each root and seeing if any of the fibers contain an `actualDuration` attribute,

The problem is that the `actualDuration` attribute will be present on v16.4 fibers, which pre-date PR #13058. As a result, the Profiler UI may enable itself with versions of React that it cannot work correctly with.

Perhaps an easy solution would be to rename one of the `unstable_Profiler`'s fiber attributes prior to the next minor release (e.g. `treeBaseTime` -> `treeBaseDuration`) and change the DevTools Profiler to feature check using this new name instead.
invariant(
        false,
        'Element type is invalid: expected a string (for built-in ' +
          'components) or a class/function (for composite components) ' +
          'but got: %s.%s',
        type == null ? type : typeof type,
        info,
      );
    }
  }
}
export function createFiberFromFragment(
  elements: ReactFragment,
  mode: TypeOfMode,
  expirationTime: ExpirationTime,
  key: null | string,
): Fiber {
  const fiber = createFiber(Fragment, elements, key, mode);
  fiber.expirationTime = expirationTime;
  return fiber;
}
export function createFiberFromProfiler(
  pendingProps: any,
  mode: TypeOfMode,
  expirationTime: ExpirationTime,
  key: null | string,
): Fiber {
  if (__DEV__) {
    if (
      typeof pendingProps.id !== 'string' ||