[LayoutNG] flag-specific rebaselines for css2.1

For the following 2 tests, their test blocks render
correctly, but fail because its LayoutNG uses different
font for spaces in the ref block. LayoutNG segments whole
paragraph, and that fonts for the space characters may be
affected by surrounding characters.

  css2.1/t1202-counter-04-b.html
  css2.1/t1202-counters-04-b.html

TBR=eae@chromium.org
NOTRY=true

Bug: 591099
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_layout_ng
Change-Id: I8f2bdc838bf00355cbed18786080f727c41eea66
Reviewed-on: https://chromium-review.googlesource.com/1142046
Commit-Queue: Koji Ishii <kojii@chromium.org>
Reviewed-by: Koji Ishii <kojii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576080}
5 files changed