GitLab

Change the runtime flag status to "experimental", and remove
virtual/layout_ng_fieldset/.

Known issues:

* inert-retargetting*.tentative.html:
  They have CHECK failures in |NGPhysicalBoxFragment::
  CheckSameForSimplifiedLayout()|

* contain-intrinsic-size-014.html: Fieldset NG doesn't support size
  containment yet.

* fieldset-mask.html: Fieldset NG needs to adjust mask painting area.

We'll address them soon.

Bug: 375693, 875235
Change-Id: Id051f04c7e0fe862e26305b27c106abdee75ba1e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2340647Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Auto-Submit: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795951}