Revert of Make /deep/ as no-op and remove ::shadow in dynamic profile (patchset #9 id:160001 of https://codereview.chromium.org/2778983006/ )

Reason for revert:
(from the right account this time) Completely breaks Chrome OS login UI

Original issue's description:
> Make /deep/ as no-op and remove ::shadow in dynamic profile
>
> Intent to Remove: https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/HX5Y8Ykr5Ns
>
> To make this CL small one, and easy to be reverted, all tests which depend on /deep/
> (or ::shadow) were either removed or updated in another CL:
> https://bugs.chromium.org/p/chromium/issues/detail?id=715034.
>
> This CL only touched the small part so that users can't use /deep/ or ::shadow
> in CSS dynamic profile in M60. The further internal clean up is needed in other CLs.
>
> BUG=489954
>
> Review-Url: https://codereview.chromium.org/2778983006
> Cr-Commit-Position: refs/heads/master@{#471684}
> Committed: https://chromium.googlesource.com/chromium/src/+/a7ab8a110bd6b5339c03a34a5a6bb9a419a49e60

TBR=achuith@chromium.org,alemate@chromium.org,kochi@chromium.org,hayato@chromium.org
# Not skipping CQ checks because original CL landed more than 1 days ago.
BUG=489954

Review-Url: https://codereview.chromium.org/2885153003
Cr-Commit-Position: refs/heads/master@{#472295}
12 files changed