Add UseCounter for cursor size

Large cursors with transparency are being used to trick users on
abusive sites (see bug for more details). This CL adds use counters
to track how often large (> 32x32) and small (<= 32x32) custom images
are used on the web.

Bug: 880863
Change-Id: I631e308f08cd8a14d74fa9d9b6f08821e2839d03
Reviewed-on: https://chromium-review.googlesource.com/c/1272097
Reviewed-by: Avi Drissman <avi@chromium.org>
Reviewed-by: Rick Byers <rbyers@chromium.org>
Commit-Queue: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#598541}
3 files changed