(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.
} while (node !== null);
  return null;
}
function scheduleWork(fiber: Fiber, expirationTime: ExpirationTime) {
  recordScheduleUpdate();
  if (__DEV__) {
    if (fiber.tag === ClassComponent) {
      const instance = fiber.stateNode;
      warnAboutInvalidUpdates(instance);
    }
  }
  const root = scheduleWorkToRoot(fiber, expirationTime);
  if (root === null) {
    if (__DEV__ && fiber.tag === ClassComponent) {
      warnAboutUpdateOnUnmounted(fiber);
    }
    return;
  }
  if (
    !isWorking &&
    nextRenderExpirationTime !== NoWork &&
    expirationTime < nextRenderExpirationTime
  ) {
    
    interruptedBy = fiber;
    resetStack();
  }
  markPendingPriorityLevel(root, expirationTime);
  if (