GitLab

 - Only updating the DICE enabled codepath (sync_confirmation.html),
   and related tests.
 - Forking signin_shared_css.html so that the old (Polymer2) version
   of it can still be used by the pages that are not migrated yet.
 - Drive-by: Added type-checking target for
   sync_disabled_confirmation.js which was missing.

Bug: 965770
Test: Page still works, no more HTML imports warnings in DevTools.
Change-Id: I714e4d539316f21d7f45c8516c0c4175c267c149
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1848348Reviewed-by: John Lee <johntlee@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Reviewed-by: Thomas Tangl <tangltom@chromium.org>
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#705637}