Avoid recursing in the FragmentData destructor

Too deep recursions can cause stack overflows.

Bug: 874759
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ie532e28bceee4e7f1c3ab501b80c0e2f14be083a
Reviewed-on: https://chromium-review.googlesource.com/1106378
Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#583657}
2 files changed