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There are currently 2 ways in which the ClientToServerResponse proto
may signal an error [1][2]. Sync.PostedClientToServerMessageError used
to consider only one of them, causing some buckets to be empty. This
CL introduces a new version of the histogram which records the metric
correctly.

The old histogram is kept around for the moment so the two can be
compared side by side once the new histogram reaches Stable. It will
be deprecated after this.

[1] https://source.chromium.org/chromium/chromium/src/+/b90d88871c6e4f9c44a1f19d244c3e1632ae26de:components/sync/protocol/sync.proto;l=975
[2] https://source.chromium.org/chromium/chromium/src/+/b90d88871c6e4f9c44a1f19d244c3e1632ae26de:components/sync/protocol/sync.proto;l=953

Bug: 1004302
Change-Id: I6d56061bc032664a1c0a3c303f8ccdd39f60e749
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2584003
Commit-Queue: Caitlin Fischer <caitlinfischer@google.com>
Reviewed-by: Caitlin Fischer <caitlinfischer@google.com>
Reviewed-by: Marc Treib <treib@chromium.org>
Auto-Submit: Victor Vianna <victorvianna@google.com>
Cr-Commit-Position: refs/heads/master@{#836596}