GitLab

Add UMA stats for reasons that veto the checkering of an image.

Change-Id: I0626c200152e0bfa9f8a29e8595d062628631b4a
Reviewed-on: https://chromium-review.googlesource.com/566064
Commit-Queue: Khushal <khushalsagar@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Vladimir Levin <vmpstr@chromium.org>
Reviewed-by: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#486057}