(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.
const instance = finishedWork.stateNode;
    let instanceToUse;
    switch (finishedWork.tag) {
      case HostComponent:
        instanceToUse = getPublicInstance(instance);
        break;
      default:
        instanceToUse = instance;
    }
    if (typeof ref === 'function') {
      ref(instanceToUse);
    } else {
      if (__DEV__) {
        if (!ref.hasOwnProperty('current')) {
          warning(
            false,
            'Unexpected ref object provided for %s. ' +
              'Use either a ref-setter function or React.createRef().%s',
            getComponentName(finishedWork),
            getStackAddendumByWorkInProgressFiber(finishedWork),
          );
        }
      }
      ref.current = instanceToUse;
    }
  }
}
function commitDetachRef(current: Fiber) {
  const currentRef = current.ref;
  if (currentRef !== null) {