(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 rendered = ReactTestRenderer.create(
      <div>
        <AdvanceTime byAmount={2} />
      </div>,
    );
    advanceTimeBy(20);
    expect(() => {
      rendered.update(
        <div ref="this-will-cause-an-error">
          <AdvanceTime byAmount={3} />
        </div>,
      );
    }).toThrow();
    advanceTimeBy(20);
    
    rendered.update(
      <div>
        <AdvanceTime byAmount={7} />
      </div>,
    );
    
    
    
    
    expect(rendered.root.findByType('div')._currentFiber().treeBaseTime).toBe(
      7,
    );
  });
});