[remoting][IT2ME] Register support host over remoting API

This CL adds a RemotingRegisterSupportHostRequest that registers an
IT2ME host using the new remoting API. This will be used for the
ChromeOS enterprise use case but the website will still use the old
XMPP-based registration request until it is updated to support that.

Bug: 962765
Change-Id: Ifcf2eb6eaba76db6386ae27f86f20e06088383f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1611023
Commit-Queue: Yuwei Huang <yuweih@chromium.org>
Reviewed-by: Joe Downing <joedow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660738}
15 files changed