Add custom cursor image size to UseCounter ukm whitelist

This API is being used for abuse.

TBR=bmcquade@chromium.org

Bug: 880863
Change-Id: I122e23f589d62eecc01a4418db3573c53779de7f
Reviewed-on: https://chromium-review.googlesource.com/c/1275165
Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Commit-Queue: Charlie Harrison <csharrison@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#599314}(cherry picked from commit 6072eb20a5d5007d5cc0a9ca316f7b23b95c660f)
Reviewed-on: https://chromium-review.googlesource.com/c/1283389
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/branch-heads/3578@{#36}
Cr-Branched-From: 4226ddf99103e493d7afb23a4c7902ee496108b6-refs/heads/master@{#599034}
1 file changed