[DL]: Prevent anchor link navigation on locked elements.

This patch renames IsDisplayLockedForFocus into
DisplayLockPreventsDiscoverability.

Also uses this function to prevent anchor link and manual js
scrollIntoView() from scrolling to elements in a locked subtree.

R=chrishtr@chromium.org

Bug: 882663
Change-Id: I1f45900d012d682bfb57b9c92cbb1739471bca84
Reviewed-on: https://chromium-review.googlesource.com/c/1435709
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#627104}
6 files changed