Revert of Make /deep/ as no-op and remove ::shadow in dynamic profile

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:
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

[rkc1, 2017-05-16 19:52:21]

The CQ bit was checked by rkc@google.com

[rkc1, 2017-05-16 19:52:21]

Created Revert of Make /deep/ as no-op and remove ::shadow in dynamic profile

[commit-bot: I haz the power, 2017-05-16 19:53:36]

CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-05-16 19:53:37]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-05-16 19:53:38]

No L-G-T-M from a valid reviewer yet.
CQ run can only be started once the patch has received an L-G-T-M from a full
committer.
Even if an L-G-T-M may have been provided, it was from a non-committer,_not_ a
full super star committer.
Committers are members of the group "project-chromium-committers".
Note that this has nothing to do with OWNERS files.