Make the `enableSchedulingProfiler` flag dynamic for the profiling build (so marks can be disabled). I think it should be sufficient to do something like:
```js
export const enableSchedulingProfiler =
  __PROFILE__ && dynamicFeatureFlags.enableSchedulingProfiler;
```

Update our User Timing API check to include `clearMeasures` and when we call `mark(name)`, also call `clearMeasures(name)` to avoid clogging the entries buffer. (Apparently this has a significant negative performance impact for Firefox.)
it('should log React version on initialization', () => {
    expect(marks).toEqual([`--react-init-${ReactVersion}`]);
  });
  
  it('should mark sync render without suspends or state updates', () => {
    ReactTestRenderer.create(<div />);
    expect(marks).toEqual([
      `--react-init-${ReactVersion}`,
      '--schedule-render-1',
      '--render-start-1',
      '--render-stop',
      '--commit-start-1',
      '--layout-effects-start-1',
      '--layout-effects-stop',
      '--commit-stop',
    ]);
  });
  
  it('should mark concurrent render without suspends or state updates', () => {
    ReactTestRenderer.create(<div />, {unstable_isConcurrent: true});
    expect(marks).toEqual([
      `--react-init-${ReactVersion}`,
      '--schedule-render-512',
    ]);
    marks.splice(0);
    expect(Scheduler).toFlushUntilNextPaint([]);
    expect(marks).toEqual([
      '--render-start-512',
      '--render-stop',