Revert "[Autofill] Use ShadowDom placeholder to preview suggestions."

This reverts commit 0727466e09c7285f3c4fe6a7974bfc68fd9bbccb.

Reason for revert: Makes some passwords be visible when suggested to the user.

Bug: 771097


Original change's description:
> [Autofill] Use ShadowDom placeholder to preview suggestions.
> 
> Bug: 753645
> Change-Id: Idabb4d01b45aa08a71f9fc8ad1dd89b192cfb0c5
> Reviewed-on: https://chromium-review.googlesource.com/646754
> Commit-Queue: Sebastien Seguin-Gagnon <sebsg@chromium.org>
> Reviewed-by: Kent Tamura <tkent@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#505743}

TBR=yosin@chromium.org,tkent@chromium.org,sebsg@chromium.org

Change-Id: I3a874ea052f598724831bdfcf0e16576a09353b4
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 753645
Reviewed-on: https://chromium-review.googlesource.com/697644
Reviewed-by: Sebastien Seguin-Gagnon <sebsg@chromium.org>
Commit-Queue: Sebastien Seguin-Gagnon <sebsg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506011}
17 files changed