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This reverts commit f02f7639.

Reason for revert: Failed to build on Cast Audio Linux

https://ci.chromium.org/p/chromium/builders/ci/Cast%20Audio%20Linux/67917

Original change's description:
> Improve DoH server availability tracking
> 
> Now that server availability and stats are tracked per-context, DoH
> servers only need to be disabled for consecutive failures. And now that
> availability behaves much more similarly to normal server failure
> tracking, the availability has been mostly merged into the normal
> tracking instead of using a separate flag.  A DoH server is now
> considered "available" (eligible for use in automatic mode) if
> |ServerStats::last_failure_count| is less than
> |kAutomaticModeFailureLimit| and there has been at least one success
> recorded on the current connection.
> 
> Net effect is that DoH servers can be enabled or failure-tracking reset
> for any successful request or probe to that server on the same context,
> even if a failure disable has taken effect (eg a transaction started
> before the server was disabled, or a new probe when we restart probes in
> a future CL).
> 
> Also, previously the DoH probe logic reset availability when restarted.
> Because the probes were generally only restarted for connection change,
> this had the effect of resetting availability for connection change.
> Now, the ResolveContext handles that itself on connection change by
> resetting the flag that it has seen at least one success on the current
> connection.
> 
> Bug: 1022059
> Change-Id: I872057cbb9f7a0a41f580dff57d906b1e4e5d33c
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2062676
> Reviewed-by: Matt Menke <mmenke@chromium.org>
> Commit-Queue: Eric Orth <ericorth@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#745551}

TBR=mmenke@chromium.org,ericorth@chromium.org

Change-Id: I0005490d361cb8c86583ab1b0f3819eeee13c4cd
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1022059
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2080446Reviewed-by: Chris Mumford <cmumford@google.com>
Commit-Queue: Chris Mumford <cmumford@google.com>
Cr-Commit-Position: refs/heads/master@{#745554}