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.)
/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow strict
 */
export const warnAboutSpreadingKeyToJSX = __VARIANT__;
export const disableInputAttributeSyncing = __VARIANT__;
export const enableFilterEmptyStringAttributesDOM = __VARIANT__;
export const enableLegacyFBSupport = __VARIANT__;
export const decoupleUpdatePriorityFromScheduler = __VARIANT__;
export const enableDebugTracing = __EXPERIMENTAL__;
export const deferRenderPhaseUpdateToNextBatch = !__VARIANT__;
export const debugRenderPhaseSideEffectsForStrictMode = __DEV__;
export const replayFailedUnitOfWorkWithInvokeGuardedCallback = __DEV__;
export const enableTrustedTypesIntegration = false;
export const disableSchedulerTimeoutBasedOnReactExpirationTime = false;
export const enableDoubleInvokingEffects = false;
export const enableUseRefAccessWarning = __VARIANT__;
export const enableProfilerNestedUpdateScheduledHook = __VARIANT__;