(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.
typeof pendingProps.onRender !== 'function'
    ) {
      invariant(
        false,
        'Profiler must specify an "id" string and "onRender" function as props',
      );
    }
  }
  const fiber = createFiber(Profiler, pendingProps, key, mode | ProfileMode);
  fiber.type = REACT_PROFILER_TYPE;
  fiber.expirationTime = expirationTime;
  return fiber;
}
export function createFiberFromText(
  content: string,
  mode: TypeOfMode,
  expirationTime: ExpirationTime,
): Fiber {
  const fiber = createFiber(HostText, content, null, mode);
  fiber.expirationTime = expirationTime;
  return fiber;
}
export function createFiberFromHostInstanceForDeletion(): Fiber {
  const fiber = createFiber(HostComponent, null, null, NoContext);
  fiber.type = 'DELETED';
  return fiber;
}
export function createFiberFromPortal(
  portal: ReactPortal,
  mode: TypeOfMode,