(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.
let node = fiber;
  do {
    const alternate = node.alternate;
    if (
      node.expirationTime === NoWork ||
      node.expirationTime > expirationTime
    ) {
      node.expirationTime = expirationTime;
      if (
        alternate !== null &&
        (alternate.expirationTime === NoWork ||
          alternate.expirationTime > expirationTime)
      ) {
        alternate.expirationTime = expirationTime;
      }
    } else if (
      alternate !== null &&
      (alternate.expirationTime === NoWork ||
        alternate.expirationTime > expirationTime)
    ) {
      alternate.expirationTime = expirationTime;
    }
    if (node.return === null && node.tag === HostRoot) {
      return node.stateNode;
    }
    node = node.return;