[LayoutNG] Avoid destroying NGListMarker in DestroyLeftoverChildren

This patch avoids destroying NGListMarker, as
DestroyLeftoverChildren() does so for non-NG ListMarker.

This fix is speculative. I could not reproduce the problem,
but this seems to be the possible cause from the crash dump.

Bug: 919764
Change-Id: I50e56ecec9e68a32fcb3eed7c4ac84ae04865a43
Reviewed-on: https://chromium-review.googlesource.com/c/1399693
Commit-Queue: Koji Ishii <kojii@chromium.org>
Commit-Queue: Emil A Eklund <eae@chromium.org>
Reviewed-by: Emil A Eklund <eae@chromium.org>
Reviewed-by: Morten Stenshorne <mstensho@chromium.org>
Cr-Commit-Position: refs/heads/master@{#620760}
1 file changed