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.)
return {
      mark(markName) {
        marks.push(markName);
      },
    };
  }
  beforeEach(() => {
    jest.resetModules();
    global.performance = createUserTimingPolyfill();
    marks = [];
    React = require('react');
    
    ReactTestRenderer = require('react-test-renderer');
    ReactNoop = require('react-noop-renderer');
    Scheduler = require('scheduler');
  });
  afterEach(() => {
    delete global.performance;
  });
  
  it('should not mark if enableSchedulingProfiler is false', () => {
    ReactTestRenderer.create(<div />);
    expect(marks).toEqual([]);
  });