ConnectJob timeout cleanup part 5: HttpProxyConnectJob revisited

Use tunnel timeout in HttpProxyConnectJob when responding to an auth
challenge from an HTTP/1.x proxy. Previously, there was no connection
timeout to this phase, which seems a bit odd, since all other connection
phases have one. At this point, we've already received a response over
the socket, so not having a timer is less problematic than not having
one for other stages, but still seems best to be consistent.

Bug: 937137
Change-Id: I09ab3923f8f3a00ddcd38da2782ee02bab07ac34
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1548369
Commit-Queue: Matt Menke <mmenke@chromium.org>
Reviewed-by: Asanka Herath <asanka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#646930}