Shared Storage: Add kSuccess bucket to SharedStorage.Worklet.Error.Type

Currently we have no success bucket for the
Storage.SharedStorage.Worklet.Error.Type histogram. We should add one
so that we can see the proportion of errors to successes.

Bug: 327239677,1218540
Change-Id: If390613e29127fbde2de1d00098a1806367138df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5328949


Reviewed-by: Yao Xiao <yaoxia@chromium.org>
Commit-Queue: Cammie Smith Barnes <cammie@chromium.org>
Reviewed-by: Ayu Ishii <ayui@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1267178}