Notes: https://docs.google.com/document/d/1SIKd6R-v0gXgSL-UmC_t_zCvyY3Hd-7C52SbLJxAxQI/edit#heading=h.kqj44lz4njsp

The plan is to migrate P2PSocketManager::GetHostAddress to use the new HostResolver::CreateRequest method and then set ResolveHostParameters.source to MULTICAST_DNS (once it is implemented) when the host name ends with ".local."

Blocked on MDNS support in HostResolver via HostResolverSource (https://cs.chromium.org/chromium/src/net/dns/host_resolver_source.h?q=846423&sq=package:chromium&g=0&l=10).

Let me know if there is a more specific bug to track.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/de5059db59ef0c9896ce918f226b3ab1db8658c5

commit de5059db59ef0c9896ce918f226b3ab1db8658c5
Author: Zach Stein <zstein@chromium.org>
Date: Thu Sep 06 04:29:56 2018

Migrate P2PSocketManager::GetHostAddress to use the new HostResolver API.

This will enable us to issue MDNS queries for .local TLDs once HostResolver
supports MDNS.

Bug:  chromium:879746 
Cq-Include-Trybots: luci.chromium.try:linux_mojo
Change-Id: I4c5a8e01c2337f83a73ac3f6ecc6d3527bdcd875
Reviewed-on: https://chromium-review.googlesource.com/1200404
Reviewed-by: Eric Orth <ericorth@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Commit-Queue: Zach Stein <zstein@google.com>
Cr-Commit-Position: refs/heads/master@{#589099}
[modify] https://crrev.com/de5059db59ef0c9896ce918f226b3ab1db8658c5/services/network/p2p/socket_manager.cc

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7562ea9e8862fe435354d08c2422a3597efc7a79

commit 7562ea9e8862fe435354d08c2422a3597efc7a79
Author: Zach Stein <zstein@chromium.org>
Date: Mon Oct 29 07:24:35 2018

Resolve hostname in P2PSocketManager with MDNS if the TLD is "local"

Bug:  chromium:879746 
Cq-Include-Trybots: luci.chromium.try:linux_mojo
Change-Id: Iabd87f6e3aad8ed689d255329310a48a7a02f323
Reviewed-on: https://chromium-review.googlesource.com/c/1217346
Commit-Queue: Zach Stein <zstein@google.com>
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#603430}
[modify] https://crrev.com/7562ea9e8862fe435354d08c2422a3597efc7a79/services/network/p2p/socket_manager.cc