Only use GetUnignoredChildAtIndex when looping over unignored children

This change also adds two tests to exercise the
GetUnignoredChildCount and GetUnignoredChildAtIndex functions.

Change-Id: I9cd5e7367356968de0ccebcdceb4068e7f904caa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1534188
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Akihiro Ota <akihiroota@chromium.org>
Cr-Commit-Position: refs/heads/master@{#643407}
2 files changed