[LayoutNG] Add FlagExpectations for LayoutNG 1/3

This patch adds the FlagExpectations file for LayoutNG.

The patch is split into 3 CLs because it hits the max limit of CQ.

There are many flaky tests that may need multiple passes until it is
stabilized.

BUG=591099

Review-Url: https://codereview.chromium.org/2827643004
Cr-Commit-Position: refs/heads/master@{#466571}
1 file changed