Add experiment of racing stale dns on connection.

In QuicStreamFactory::Job, chances are host resolution won't return synchronously. While waiting for the host resolution callback, the stale host resolver will be queried, and a connection from the stale host result will be established but not confirmed. After host resolution returns, the two IP addresses will be compared. If they match, the connection will be confirmed. Otherwise the connection from stale host will be closed and connection from the fresh resolution will be established.

Bug: 787942
Change-Id: I7a5f78ec42e97778d7c7d200f4d8ac894611fd19
Reviewed-on: https://chromium-review.googlesource.com/1186112
Commit-Queue: Renjie Tang <[email protected]>
Reviewed-by: Ryan Hamilton <[email protected]>
Cr-Commit-Position: refs/heads/master@{#594522}
13 files changed