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This keeps consistent with legacy-results.html and rebaseline bots
which treat MISSING as regressions.

Also rename "unexpected failures" to "regressions" to be consistent
with "Regressions" in summary.

Also avoid exception when some test is directly under LayoutTests/
(where some developers like me put quick local layout tests).

Change-Id: I80da6c9f54c64c98089a90ab72ae51e821a06a7b
Reviewed-on: https://chromium-review.googlesource.com/807264
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Aleks Totic <atotic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521605}