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This patch adds UMA metrics to track the stages of HaTS that users go
through. This helps keep track of number of users who view the UMA
survey. Since Chrome OS uses client side logic to roll dice for survey,
UMA metrics is required.

Test: Manually
Bug: 1134413
Change-Id: Ic4981ab97ba3f1b99a588b5a32279bfca03009d3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2444511
Commit-Queue: Malay Keshav <malaykeshav@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815314}