Expose CONNECT headers to ProxyDelegate

This brings back (slightly refreshed versions of) the
OnBeforeTunnelRequest(), OnTunnelHeadersReceived() hooks that were
removed in

These hooks are not used by the Data Reduction Proxy, because it
doesn't proxy https:// URLs.  They are restored for the benefit of those
downstream embedders (Opera) that use CONNECT tunnels to proxy HTTPS

Bug: 915659
Change-Id: Id0e120882a22a66c72802087a1775daeef661984
TBR: rockot@google.com
Reviewed-on: https://chromium-review.googlesource.com/c/1379766
Commit-Queue: Wojciech Dzier┼╝anowski <wdzierzanowski@opera.com>
Reviewed-by: Matt Menke <mmenke@chromium.org>
Reviewed-by: Tarun Bansal <tbansal@chromium.org>
Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Reviewed-by: Eric Roman <eroman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#624075}
48 files changed