(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.
case HostRoot: {
      return;
    }
    case Profiler: {
      if (enableProfilerTimer) {
        const onRender = finishedWork.memoizedProps.onRender;
        onRender(
          finishedWork.memoizedProps.id,
          current === null ? 'mount' : 'update',
          finishedWork.actualDuration,
          finishedWork.treeBaseTime,
          finishedWork.actualStartTime,
          getCommitTime(),
        );
      }
      return;
    }
    case PlaceholderComponent: {
      return;
    }
    default: {
      invariant(
        false,
        'This unit of work tag should not have side-effects. This error is ' +
          'likely caused by a bug in React. Please file an issue.',
      );
    }
  }
}
function commitResetTextContent(current: Fiber) {