DevTools: enable persistence2.0 experiment by default

This patch enables persistence2.0 experiment by default, which results
in the following changes:
- automapping will be enabled by default for all workspace users
  (automapping design doc: https://goo.gl/lqYrql)
- a new UI for workspaces will be enabled by default for all workspace
  users

BUG=277885
R=dgozman

Review-Url: https://codereview.chromium.org/2744553003
Cr-Commit-Position: refs/heads/master@{#460512}
2 files changed