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

Reland the CL [1], which was reverted at [2], since CrOS's OOBE issue was fixed.

- [1]: https://codereview.chromium.org/2778983006
- [2]: https://codereview.chromium.org/2885153003

Bug: 489954,723259
Change-Id: Ie162502385443a4e9a9cc80444c596458ad1e100
Reviewed-on: https://chromium-review.googlesource.com/575322
Reviewed-by: Takayoshi Kochi <kochi@chromium.org>
Commit-Queue: Hayato Ito <hayato@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487745}
12 files changed