[DL]: Keep track of non-searchable and locked display locks on the doc.

This patch keeps a count on the document of two things:
- Non-searchable display locks
  - This is used to early out tab order and anchor link navigation,
    since if everything is searchable then display locks don't prevent it.
- Locked display locks.
  - This is used to early out forcing updates for display locks during
    forced layouts, since if nothing is locked then nothing needs to be


Bug: 882663, 924550
Change-Id: I9c4e7be0b1a7d864e57641f46690d2d618a5b4dc
Reviewed-on: https://chromium-review.googlesource.com/c/1436536
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#627605}
7 files changed