DL: Skip recursing into display-locked elements for inspector font collection.

This patch ensures that we don't process display-locked elements when doing
font collection. In NG this can cause a DCHECK since
we might not have laid out the contents of the locked element. In general,
the contents are not painted or visible so there is no need to collect
font information on them.

R=chrishtr@chromium.org, rakina@chromium.org

Bug: 966754
Change-Id: I807eaa387f7a4893be7de9566c9c9a95181237b2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1629052
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663887}