metamask-extension/app/scripts/migrations/034.js

import { cloneDeep } from 'lodash'

const version = 34

/**
 * The purpose of this migration is to enable the {@code privacyMode} feature flag and set the user as being migrated
 * if it was {@code false}.
 */
export default {
  version,
  async migrate(originalVersionedData) {
    const versionedData = cloneDeep(originalVersionedData)
    versionedData.meta.version = version
    const state = versionedData.data
    versionedData.data = transformState(state)
    return versionedData
  },
}

function transformState(state) {
  const { PreferencesController } = state

  if (PreferencesController) {
    const featureFlags = PreferencesController.featureFlags || {}

    if (
      !featureFlags.privacyMode &&
      typeof PreferencesController.migratedPrivacyMode === 'undefined'
    ) {
      // Mark the state has being migrated and enable Privacy Mode
      PreferencesController.migratedPrivacyMode = true
      featureFlags.privacyMode = true
    }
  }

  return state
}