[LayoutNG] Add flaky results to FlagExpectations for LayoutNG

This patch adds flaky results from 5-6 iterations of running tests.

I will run a few more iterations and see how it stabilizes.

BUG=591099

Review-Url: https://codereview.chromium.org/2836883002
Cr-Commit-Position: refs/heads/master@{#466894}
1 file changed