Call CommitChange after a SVG*List.clear() operation

The SVGListPropertyTearOffHelper did not call CommitChange(), meaning
that the element wasn't notified of the change, and wouldn't invalidate
et.c as needed. It also could've failed to synchronize the attribute
properly.

Bug: 843901
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Iad581027c3748e3e90cf6fe3d944273b207fef0f
Reviewed-on: https://chromium-review.googlesource.com/1189882
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#586625}
4 files changed