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The layout tests aren't testing much at the moment, as they're never
served over HTTPS. This patch creates `.https` versions of the tests
and reworks them to actually exercise the behavior of `__Host` and
`__Secure` cookie prefixes.

Bug: 843945
Change-Id: I31968133ca8846f3ffc4faec2339e3d0d03c77f8
Reviewed-on: https://chromium-review.googlesource.com/1179150
Commit-Queue: Mike West <mkwst@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584016}