(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.
appendChildToContainer,
  insertBefore,
  insertInContainerBefore,
  removeChild,
  removeChildFromContainer,
  replaceContainerChildren,
  createContainerChildSet,
} from './ReactFiberHostConfig';
import {
  captureCommitPhaseError,
  requestCurrentTime,
  scheduleWork,
} from './ReactFiberScheduler';
import {StrictMode} from './ReactTypeOfMode';
const {
  invokeGuardedCallback,
  hasCaughtError,
  clearCaughtError,
} = ReactErrorUtils;
const emptyObject = {};
let didWarnAboutUndefinedSnapshotBeforeUpdate: Set<mixed> | null = null;
if (__DEV__) {
  didWarnAboutUndefinedSnapshotBeforeUpdate = new Set();
}
export function logError(boundary: Fiber, errorInfo: CapturedValue<mixed>) {
  const source = errorInfo.source;
  let stack = errorInfo.stack;
  if (stack === null && source !== null) {
    stack = getStackAddendumByWorkInProgressFiber(source);
  }