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This cl adds two histograms for the AccountPickerBottomSheet
Signin.AccountConsistencyPromoAction.Shown.Count - logged every
time the bottom sheet is shown to the user. Records number of times
bottom sheet was shown previously.
Signin.AccountConsistencyPromoAction.SignedIn.Count - logged when
the user signs in using the bottom sheet. Records number of times bottom
sheet was shown previously.

A new shared preference is also introduced to keep track of how many
times the bottom sheet is shown.

Bug: 1153093
Change-Id: I6a0bcc37dddfc107cbc89516ad5d6161c781faba
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2574849Reviewed-by: Egor Pasko <pasko@chromium.org>
Reviewed-by: Alice Wang <aliceywang@chromium.org>
Reviewed-by: Alex Ilin <alexilin@chromium.org>
Commit-Queue: Tanmoy Mollik <triploblastic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#838014}