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Tasks associated with transactions are terminated when a dispatcher
host's connection goes away, but queued connection open/delete
requests are not associated with transactions, meaning attempting to
send the results will fail. To avoid this, check to see if the
dispatcher is still connected when a request gets to the head of the
queue.

BUG=650635
R=cmumford@chromium.org

Review-Url: https://codereview.chromium.org/2386683003
Cr-Commit-Position: refs/heads/master@{#422840}